Phalacrognathus Muelleri
Phalacrognathus muelleri beetles are found wild in Queensland, Australia. They are more commonly known as rainbow stag beetles because of their colorful armor.
They are very popular with beetle collectors because they are such a beautiful beetle and they have a fairly long life. They easily live for one year, but can also live for up to two years if you take good care of them. They are not an aggressive beetle, which makes them popular pets for people who have younger children. Their mandibles are not very strong. If your finger gets caught between the mandibles, you will feel a slight pressure, but it does not hurt and will not draw blood. The only thing you need to be careful of is their fishhook nails. They do have a strong vicelike grip and when they hold onto little fingers, they are very difficult to get off. If you try to pull them off, their nails can pierce the skin. For bigger hands, if you leave them in your palm, they have nothing to grip onto and are easy to remove. |
Male Rainbow Stag Beetles vs. Female Rainbow Stag Beetles
Male rainbow stag beetles generally have long, curved mandibles, although the smaller males can have short mandibles. The male uses his mandibles to scoop up and fling other beetles when they fight. Males can reach a size of 68 mm in the wild.
The females have much smaller mandibles that are good for breaking down wood. Females also have a line down the middle of their head, so this is an easy way to identify a female. They can reach a size of 45 mm. |
Main Types of Rainbow Stag Beetles
Normal type. This is the type that gave the beetle its name and is the most common. Its armor looks like it has a rainbow on it.
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Red type. Most of its armor is a reddish color. Some have a very dark red color.
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Green type. This type is just plain green. It doesn't have the rainbow colors on it.
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Black type. It is more of a dark brown color than black. This is one of the most coveted types of rainbow stag beetles by beetle collectors because it is not so common.
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Eye Color Variation
On rare occasions, rainbow stag beetles have white eyes. This is most common on the green type. These beetles are able to pass this trait on to their offspring. It is a recessive gene.
The male to the left is 56 mm and the female is 38 mm. The price of rainbow stag beetles depends on its armor's color, eye color and the size of the male. The black type is usually the most expensive, with the normal type being the cheapest. Males which are bigger than 60mm are also very expensive. |
Caring for Rainbow Stag Beetles
Rainbow stag beetles are very easy to look after. Even though they come from Queensland where it is warm all year round, they are quite resilient to lower and higher temperatures. The optimum temperature for the adult beetle is between 22 and 27 degrees Celsius, but they have no problem surviving through a Japanese winter where the temperatures are lower than 10 degrees Celsius. During this time, they are not very active and will generally just hide in the humus without eating until it gets warmer. They can also survive the very hot summers in Japan, where the temperatures regularly reach over 30 degrees Celsius.
There are a few supplies that you will need. Japan has a big beetle culture, so it is easy to purchase items specifically designed for beetles.
The containers above are very popular with beetle enthusiasts. They come in five sizes. Beneath the thin filter paper on top are many little holes that allow air to flow in and out. Air can move through this filter, but it prevents fruit flies from entering. In summer, fruit flies can be a big problem in Japan. These containers are also very good for keeping the humidity level high, which is important when looking after rainbow stag beetles. Since the air in the container does remain moist for a long time, mold does tend to grow on the wood if you added too much water. Containers that become dry very quickly need to be kept moist. This can be achieved by spraying in a bit of water on a daily basis.
You can purchase different mattings suitable for rainbow stag beetles in Japan. Most matting can be used for all stag beetles. You should put enough humus in the container so that the rainbow stag beetles can bury themselves in it. In summer, mites can be a big problem and are often found in the humus. Mites can begin to attach to the rainbow stag beetles around the mouth and its joints. Too many mites can weaken the beetle. A way to overcome the mite problem is to use matting that is made from a blend of coniferous trees. Mites do not like this smell. All matting needs to be kept slightly moist.
In addition to the matting, rainbow stag beetles need pieces of wood to climb on and hide beneath. These can be purchased from many shops. You can also use wood that you find outside, but you will need to kill off other insects and pests that may be on it. A lot of the wood that you can purchase also act as jelly holders. The jelly is specifically made for beetles. The beetle jelly comes in a range of flavors, such as black sugar, melon and even cola. However, beetle enthusiasts tend to buy the white jelly above because it is high in protein and is believed to lengthen the life of beetles. However, rainbow stag beetles also enjoy bananas and other fruit. Do not use fruit that has a high water content, such as watermelons. |
It is important to evenly spread out the sticks and other pieces of wood around the container so that the rainbow stag beetles can use them to move around and also help them to get back on their legs when they occasionally fall onto their backs.
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Male and female rainbow stag beetles generally get along fine with each other and can be put together in a medium sized container. Make sure there are a couple of locations to get their food and also places for the female to hide. The male will usually position himself at the food source and remain there for extended periods of time. Occasionally, the female or the male will lose the base of their leg when they become involved in a fight.
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Most beetle breeders keep the male and female beetles in separate containers or put in a separator that can be purchased for some containers. They do this to keep their beetles in perfect condition, which tends to increase their life longevity and avoids accidental loss of limbs. When you pay a lot of money for a pair of beetles, it is best to keep them separate unless you are ready to breed them.
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If you have a very large container, you can put in one male and two to three females. You should never put two males together in the same container, as they will constantly fight for mating and food rights.
The female beetles tend to get along fine with each other, but there will be cases where they will chase each other around and fight. Even though their mandibles are much smaller, they can still pick each other up. |
Unfortunately, some rainbow stag beetles are completely incompatible with each other. Some males will constantly throw the females around if they are in the same container. If this happens, they should be separated before any damage is done.
Rainbow stag beetles, both male and female, will also attack other rainbow stag beetles that are old, weak and/or deformed. You could wake up in the morning to find one of your beetles has been decapitated by the other. |
Breeding Rainbow Stag Beetles
Rainbow stag beetles become sexually mature after a few months as an adult. For the female to lay eggs, the optimum temperature is about 24 degrees Celsius. The male will mount the female to fertilize the eggs inside the female. A male can mount a female for over three hours at a time.
If you breed a normal type male with a normal type female, their offspring will also be normal type. The same will happen for the other types, so you will know what type most of the larvae will turn into. However, if you mix the types, you will create beetles with slightly different characteristics. If you kept your rainbow stag beetles in the same container, the female is probably ready to lay her eggs provided the temperature is about 24 degrees Celsius. If you kept the male and female in different containers, you will need to put them together for about two weeks to guarantee the eggs of the female will be fertilized. |
Egg Laying Method 1 for Rainbow Stag Beetles
Female rainbow stag beetles are not very fussy when it comes to laying their eggs, provided the temperature is right. Below is a method I have used for a few years with good results. Using a medium sized container, the female will lay between eight to thirty eggs. However, some females will not lay any eggs at all, even when the conditions are optimal. You will generally find that the females in their first year will lay more eggs than beetles who are nearing the end of their life.
Use a container that is about 15 cm deep. Use your fist or a glass to compact the humus in the container to a depth of about 5 cm. Most of the eggs the female will lay will be in this area. Any humus that is for stag beetles is suitable. The finer the humus, the better it is.
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Fill the container with another 8 cm of humus, allowing a little space at the top. You don't need to compact this humus. Make sure the humus is moist, but not really wet. It is better to be on the dry side than the wet side. Put in the beetle jelly and add your female rainbow stag beetle.
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The optimum temperature for egg laying is 24 degrees Celsius. Leave the female in this container for two to three weeks. Replace the jelly if she has eaten it all. However, in my experience, a female who stays in the humus and doesn't eat anything for that time is more likely to be laying eggs. The female shown above is a dark red type.
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After you have removed the female from the egg laying container, it is a good idea to just leave the eggs, if there are any, alone. If you are lucky, the female may have laid some eggs on the side or bottom of the container which are easy to see.
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Egg Laying Method 2 for Rainbow Stag Beetles
For many stag beetles, you need to put large pieces of wood into the container for the females to lay their eggs in. This is especially the case for Dorcus stag beetles. This method can also be used for rainbow stag beetles, but it is more costly and requires more effort. I recommend the method explained above, but here is another method you can use if you are interested in something different.
You will need to purchase some pieces of oak. You can use wood you have found, but it needs to be heat treated.
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Put two to three pieces of the oak wood into a container filled with water. Allow the wood to soak between half a day to a whole day.
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Use a flathead screwdriver to remove the outer bark.
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Allow time for your pieces of wood to dry.
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Use your fist or a glass jar to compact humus to a depth of 5 cm in a medium sized container.
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Place two to three pieces of wood on top of the compacted humus.
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Add humus around the wood so that only the top of the wood can be seen.
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Add beetle jelly to the container. Put in your female and leave her there for about a month.
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Caring for the Larvae
A few weeks after removing the female, you can carefully look through the humus. Even if the female laid eggs, if the temperature is too cold, the eggs will not turn into larvae.
If you find any larvae, you can transfer them along with the humus to 800 mL containers. You can continue to leave them together in the original container if you wish, but if you are interested in growing large larvae, it is best to keep them in individual containers. |
You should keep the 800 mL containers in a dark, quiet place. To allow maximum growth, you need to try and keep the temperature between 20 and 24 degrees Celsius. This can be challenging. In winter you need to use a heat source and in summer you need to use the air conditioner. If you don't care about the size of your beetle, then this is not so important, as most larvae can survive in colder and hotter conditions. You may find some will die off if the conditions are too extreme.
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Larvae go through three stages known as instars. These larvae are third instar larvae. Rainbow stag beetles are usually larvae for about a year before they start to pupate.
Large larvae will eat a lot of humus, so you will need to keep it topped up in their containers. At least twice a year, you should replace most of the humus, as it will contain a lot of feces. |
When you change the humus, leave about 20% of the original humus in the container. This is to prevent the larva from becoming shocked with the change in their environment. If the change is too extreme, the larva can become sick and/or die.
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Top the rest of the 800 mL container with new humus. This will provide lots of fresh food for the larvae. The old humus was probably full of feces, which can inhibit the growth of the larvae.
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Use your hand to make a small hole in the humus and place the larva in the middle. Some sources say that larvae find the touch of your hands very hot. If you are worried about this, use a plastic spoon to move it.
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You can cover the larva with a little bit of humus, but generally the larvae will make their own way into the humus.
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After about a year as a larva, it will start to make a pupa chamber. When the chamber is complete, the larva becomes very inactive and starts to fatten up.
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The larva will become a pupa and remain this way for about a month. Don't disturb the pupa, as this is a very delicate stage. They should be left alone in a dark, quiet location as close to the optimum 24 degrees Celsius as possible.
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On some occasions, the larva won't make a pupa chamber and it will become a pupa on top of the humus, like this female. This is not desirable. This might happen if you changed the humus too late, or if the larva didn't think there was enough room, or if the humus is too dry.
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On other occasions, the larva may have built a pupa chamber correctly, but it collapsed. You will need to carefully take out the pupa and make another chamber for it on top of the humus.
When the males become a pupa, their mandibles are curved. They straighten as they become an adult. The male's heads are also larger than the female's. Pupae look white when the larvae first pupate. Over time they will turn an orange color. |
As the pupa becomes an adult, its hind wings need to dry before the elytra begins to cover them fully. This male was the pupa from the picture to the left. Usually, this stage should occur in its original pupa chamber. The head starts off red and the elytra are white. Touching the beetle at this stage will lead to deformities, as it is very soft. Over a couple of days, the color changes into the beautiful rainbow. The rainbow stag beetle will stay in its pupa chamber for about a month, even after its exoskeleton has fully hardened. Don't rush them out. Just leave some jelly in the container and they will come out when they are ready.
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Some More Challenges You Will Encounter
Unfortunately, sometimes you will run into some problems in the pupa stage, or as the pupa is becoming an adult. The photos to the left show the two main problems. Sometimes the pupa will die, or the elytra don't form properly when the pupa becomes an adult.
I have noticed that the wings sometimes don't form properly when the temperatures are much higher than the optimum 24 degrees Celsius. It also tends to happen more with the males. There are far less problems with the females. |
I have also noticed that the elytra won't form properly if the larva has built its pupa chamber on the bottom of the beetle container. As the beetle emerges after the pupa stage, it struggles to grip onto the smooth, slippery plastic container flooring. As a result, it experiences difficulty moving into the positions it needs to as its wings form, causing some deformities.
Also, there will be some cases where adults, that look entirely healthy, will die in the first couple of months after breaking out of their pupal casings. You can reduce the risk of this sudden death by simply being patient. One main cause of this sudden death is if you break the beetle's pupa chamber to remove the adult too quickly and then excessively handle it, which can cause the beetle to become shocked. If this occurs, you will not notice anything immediately different, but the beetle can die about two months later. Ideally, you should leave the adults in their pupae chambers for 1 to 2 months after they emerge from their pupal casing, where it will remain dormant. When it is ready, it will make its own way out of the chamber and will be less susceptible to sudden death.
Another cause of sudden death, when the beetle becomes an adult, is when you pair the beetles too early for breeding. For rainbow stag beetles, if you pair them before they are 3 months old, which is when they become sexually mature, there is a higher risk of sudden death. This could also be due to shock or simply overstimulating them at too young an age. Once again, the death will occur within the next couple of months, so it is not immediately obvious that any harm is done. Remember, for this breed of beetle, it is not unreasonable for them to live up to 2 years of age, so a rainbow stag beetle dying in the first few months is very premature.
Finally, some adult beetles will die quickly if the temperatures are too high, or too low. Even though these beetles are resilient to extreme conditions, it is best to try and keep the temperatures between 23 and 28 degrees Celsius, especially in their early stages of adulthood.
The information you have just read is the cause for sudden death cases of your beetles. Of course, even if you do break the pupae chambers early and excessively handle them within the first couple of months, most will still live a long life. However, the risk of sudden death does increase if you are too eager to interact and breed your beetles (of which I have been guilty of.)
Also, there will be some cases where adults, that look entirely healthy, will die in the first couple of months after breaking out of their pupal casings. You can reduce the risk of this sudden death by simply being patient. One main cause of this sudden death is if you break the beetle's pupa chamber to remove the adult too quickly and then excessively handle it, which can cause the beetle to become shocked. If this occurs, you will not notice anything immediately different, but the beetle can die about two months later. Ideally, you should leave the adults in their pupae chambers for 1 to 2 months after they emerge from their pupal casing, where it will remain dormant. When it is ready, it will make its own way out of the chamber and will be less susceptible to sudden death.
Another cause of sudden death, when the beetle becomes an adult, is when you pair the beetles too early for breeding. For rainbow stag beetles, if you pair them before they are 3 months old, which is when they become sexually mature, there is a higher risk of sudden death. This could also be due to shock or simply overstimulating them at too young an age. Once again, the death will occur within the next couple of months, so it is not immediately obvious that any harm is done. Remember, for this breed of beetle, it is not unreasonable for them to live up to 2 years of age, so a rainbow stag beetle dying in the first few months is very premature.
Finally, some adult beetles will die quickly if the temperatures are too high, or too low. Even though these beetles are resilient to extreme conditions, it is best to try and keep the temperatures between 23 and 28 degrees Celsius, especially in their early stages of adulthood.
The information you have just read is the cause for sudden death cases of your beetles. Of course, even if you do break the pupae chambers early and excessively handle them within the first couple of months, most will still live a long life. However, the risk of sudden death does increase if you are too eager to interact and breed your beetles (of which I have been guilty of.)
Breeding Big and Small Rainbow Stag Beetles
If you want to breed large rainbow stag beetles, you need to keep the larvae in a room that is constantly 24 degrees Celsius. As a bit of an experiment, I let some of my larvae deal with the hot Japanese summer and the cold winter. The females tended to be average in size, but the males were very small. They were almost the same size as the females. They had very small mandibles, too. The only real way to tell them apart was by looking at their head. Only the females have a line that goes down the middle of their head. This activity showed that temperature does influence the size of the adult beetle. You can see this in the photo to the right.
Temperature is not the only factor affecting the size of the rainbow stag beetle. Other main reasons include using a poor substrate, using too small a container and not keeping the substrate moist. |
Below is a great way that my brother-in-law showed me to keep the temperature in the optimal range for rainbow stag beetles and other exotic beetles during the winter months.
To keep the larvae warmer than room temperature in winter, you will need a heater panel, a thermostat, a thermometer and a Styrofoam cooler box. The heater panel and thermostat are intended for use with reptiles, but they can do the same job for larvae. It is useful to have a digital thermometer that can measure the temperature inside the cooler box, as well as out. The cooler box I chose was designed for vegetables and has a gap on the sides already built in so that air can enter the box and also the wires from the thermostat and thermometer can easily be put in. Tape the wires to the inside of the box and stand the heater plate on one side. For rainbow stag beetles, you should put the thermostat to 24 degrees Celsius. However, if you are using the box for other beetle varieties as well, 22 degrees Celsius is a safe temperature to satisfy most larvae.
If you want really large males, you should look at using kinshi bottles. "Kinshi" means hypha, which is the structure used to make fungus.
The most common brand is the G-pot. Here are the instructions as written on the G-pot bottle. When using a kinshi bottle, use a spoon to dig a small hole in the middle.
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Put the larva in the hole you made with the spoon. It is best to use the 900cc bottle when the larva is at the second instar stage.
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Keep the bottle with the lid facing up for three days to make sure the larva goes inside the bottle.
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If the larva has moved inside, turn the bottle the other way. Check every few days.to see if the larva has stayed inside. You will need to change the kinshi bottle after 60% to 70% of the hypha has been eaten.
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Rainbow Stag Beetle Breeding Challenge (My Red Type Story)
In 2015 I bought a large red type rainbow stag beetle pair from a specialist beetle shop in Japan. The male was 62mm long, as seen in the picture below. In spring of 2016, I paired them together and attempted to breed them. The female laid some eggs, of which three hatched into larvae. I used the egg laying method 1, as described above.
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I kept these three larvae in 800mL containers, using the humus I bought for stag beetle larvae. I changed the humus when I noticed a lot of feces building up in the containers. However, I didn't worry about the temperature. These larvae endured the hot Japanese summer, where it regularly went above 30 degrees Celsius, and they endured cold winter temperatures that regularly went below 10 degrees Celsius.
In spring of 2017, the three larvae became pupae and eventually emerged as adults. There were two females, each about 40mm long and an extremely small male that was only 34mm long. I wondered if such a small male could successfully mate with a larger female. If that was possible, I wanted to see if the size of the parent beetles affected the size of its offspring. Would the offspring also be small, or was it possible to make them large by carefully controlling the environmental conditions? |
In spring of 2018, I paired the small male with one of the females. Above is a picture of this pairing. I left them in the same container together for a month. Then, I used the egg laying 1 method I described above. The container I used was 1.4L in size.
I left the female in the egg laying container for another month, with temperatures around the 23-25 degrees Celsius mark. |
In an attempt to make big beetles, I put each larva into separate 550cc kinshi bottles with a little bit of the humus that they were initially living in.
Throughout the summer months, I kept the temperature as close as I could to the optimal 24 degrees Celsius by using the air conditioner during the day. In the winter months, I kept the larvae in the Styrofoam cooler box I described above at a temperature of 23 degrees Celsius. I kept a careful eye on the kinshi bottles throughout the year. When about 70% of the hypha had been eaten, I put the larvae into new kinshi bottles. I moved the larger larvae to 900cc bottles, as these were most likely males. If the larvae were small, it meant they were probably female, so I just put these larvae into new 550cc kinshi bottles. Most larvae went through three or four kinshi bottles before they became pupae. |
Of the fifteen larvae that I had been caring for, twelve emerged as healthy adults after the pupa stage in the spring of 2019. There were seven males and five females. The largest male was 62mm long, which equaled the size of his grandfather and made him 28mm larger than his father.
This activity showed me that environmental conditions have the biggest influence over the size of beetles. It showed that the male rainbow stag beetles that are raised and are carefully monitored in kinshi bottles that are kept around the 24 degrees Celsius mark will be much larger than the males that are raised in humus with temperatures that greatly fluctuate throughout the year. However, for female rainbow stag beetles, the size differences between the two techniques was negligible. Whether they were raised in humus or kinshi bottles, and whether the temperature was kept at the optimal 24 degrees Celsius or allowed to fluctuate, the sizes of the females were almost the same. Therefore, it can be concluded that even if the parent beetles are small, they can produce large male offspring, if these offspring grow in the favorable environmental conditions outlined above. So did the parent beetles have any effect on the offspring? I found this analysis to be very interesting. For the males, four of the seven beetles were easily recognized as the red type. For the females, three of the five beetles showed the red type coloration. However, two of the males and two of the females showed the black type coloration. After doing some research, I found that in some cases, red type parents will produce black type, or sometimes known as dark red, offspring. This seems to occur more often when the offspring of the same parents are paired together and then the offspring of those offspring are paired together. |
These black type offspring, both male and female, were also smaller in size than the red type offspring. The black males both measured in the 50-54mm range when compared to the red type males that all measured in the 55-62mm range. The size difference in the females was not as noticeable, but the red type offspring were still a couple of millimeters bigger than the black type beetles.
The one real surprise was the largest male, which was more green in color and even showed glimpses of blue. I am unable to explain why this occurred. Below, I have included more photos to show the differences in some of the beetles. On some of the elytra, you will notice slight dimples. These occurred as the pupae became adults. The material in the kinshi bottles can be quite hard, and if it pushes into the beetle as its wings are forming, it leaves these dimples. This greatly reduces the value of these beetles, as collectors want the perfect specimen. |
Buying Rainbow Stag Beetles
How old is it?
The department store staff probably won't be able to answer this, but the larger pet shops and specialized beetle shops should have this information, because these are the kinds of records they put on the labels attached to the containers. If they can't tell you, be a little wary. Look for rainbow stag beetles that are just over three months old. These beetles are now sexually mature and active. You want to avoid adult beetles that have just emerged, as these beetles are still susceptible to sudden death. Some shops also have no problems selling rainbow stag beetles that are over 1 year old for full price. You may still get another year out of these beetles, but it may be a little more challenging to breed them. The shops may have already used the female to lay eggs. Unlike the Japanese rhinoceros beetle female that dies when it lays its eggs, rainbow stag beetle females can lay eggs over and over again, but the life of a female that has already laid eggs will be slightly reduced. |
Is the beetle missing any legs?
Avoid beetles that are missing legs. Ask to inspect the beetle before purchasing it. Rainbow stag beetles tend to lose legs when they are getting old and are nearing the end of their life. They may have also lost legs if they have not been cared for properly. Once beetles lose the base of their legs, it makes it difficult for them to climb on wood or dig through the humus. If they fall on their back, it is also extremely difficult for them to turn over again. |