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Gymnetis caseyi questions— good first beetle?

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Hi, all,


I'm just getting into beetles, and I found one that I think I'd like to try keeping, but I have a lot of questions that I haven't been able to find answers to elsewhere. The Harlequin Flower Beetle (Gymnetis caseyi) is the thing I've been looking at. It appears to be sizeable but not intimidating (I have never kept insects other than bees), diurnal, pretty easy to rear from larvae, and a vegetarian (which saves the step of keeping a colony of prey for it). I have found little information about this specific species, likely because it's a very large genus.


Does this seem like a reasonable first beetle? Are there any books or must-read literature you could recommend, regarding pet beetles generally or G. caseyi specifically? How long do they live as adults? How many should I keep in one enclosure, and how large of a habitat do they need? Will they be stressed if they live alone vs. with others, and does the sex of the other individuals matter in terms of compatibility as cagemates? Can the larvae be sexed visually? Should I start with more than one larvae? What temperature should the substrate be kept at? Do they make any noise? What pests, if any, are they vulnerable to? Is a five gallon aquarium an alright size for these beetles?


I know that's a ton of questions; if you happen to have any answers for me, especially in regards to further reading, I'd appreciate it!




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They're a great beetle to start with, one of the first that I got. Orin McMonigle's book on beetles is a great resource with a section on flower beetles but I wouldn't say its necessary to keep these guys. Definitely informative if you want to keep a few different kinds of beetles though!


I'm not sure on lifespan in general but mine have been going for months and are on their second round of egg-laying. I have a handful in a small tank (about 2.5 gallons, I guess?) and you could easily have many more in a 5 or ten gallon. They're very communal and are always feeding together, sex doesn't seem to matter and I have never tried to sex mine (or the larvae). I'd suggest starting with a small group of larvae, 3-5 or so if you want to see how you like them.


I keep mine at room temperature on the leaflitter mix from BugsInCyberspace, misting every day although that's probably not necessary if you live in a humid climate. I'm in the desert so I have to pay attention to keep things moist. Only pest problems I've had are a nematode issue when I had the substrate compacted too much -- keeping it loose got rid of that problem.


The beetles are mostly silent, although they startled me the first time they flew! They make a rather loud buzzing sound. However, they don't fly very often and are very clumsy about it when they do.

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Gynetis caseyi is one of the easiest of all flower scarabs to rear - it's quite prolific and not very particular about substrate composition. Even a good, commercially-produced organic compost will work just fine for them, so long as you periodically place a few slices of apple on the substrate surface for the larvae to eat. The adult beetles will also eat apple, as well as pear, banana or cantaloupe.

Adults can be quite long-lived if well cared for - up to 8 months or more in some cases, but the average lifespan is around 6 months.

I've reared at least 15 or more generations of G. caseyi, and have been keeping with this species continuously since 2002. They can go through their entire life cycle in a small terrarium. All you really need is a medium-sized plastic box, such as this one. Retaining humidity in the substrate is important, so ventilation should be rather minimal (but not too minimal).


Will they be stressed if they live alone vs. with others, and does the sex of the other individuals matter in terms of compatibility as cagemates?

A single caseyi won't mind living alone, but you can keep a reasonably large number of them together without any problems. This species does not fight.

Can the larvae be sexed visually?

Yes, but you'll probably need a magnifying lens, since Gymnetis larvae are rather small -

Should I start with more than one larvae?

It really all depends on whether you want to get reproduction, or just make keeping them a more temporary project. A group of 8 to 10 larvae would likely be adequate as a starter group if you want to produce a culture. If starting out with adults instead, probably 6 would be enough.

What temperature should the substrate be kept at?

This species is semi-temperate, and won't mind typical, seasonal changes in indoor temperature. Anything between 65-80 F. is fine. Optimal temperature would be approximately 75-77 F.

Do they make any noise?

None, apart from a minor buzzing when they fly, but they don't tend to fly in captivity unless in a very large terrarium with plenty of flight space.

What pests, if any, are they vulnerable to?

You're not likely at all to have any problems with pests that attack the beetles directly, but there is a potential for pests that come after the food sources (fruit and substrate) provided to the adult beetles and their larvae. Fruit flies can appear, if the fruit isn't changed out for fresh quite often enough. Grain mites, if the substrate becomes over-saturated with nutrients from overfeeding. Nematodes, again usually due to overfeeding. Fungus gnats (the larvae of which feed on the beetle's substrate) can sometimes be an issue. However, all of the above can be prevented or controlled with proper management.

Is a five gallon aquarium an alright size for these beetles?

Yes, that will certainly be large enough.

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Thanks guys! This sounds totally doable!


I know I'm getting ahead of myself here, but: it's my understanding that if I keep a group in the same enclosure, they will breed freely with one another regardless of whether or not they are consanguine (and I would imagine that if I get them all from the same supplier, they will be directly related, maybe siblings or half-siblings). Is that a problem if it happens over successive generations with a relatively small, closed population? I know that this can intensify traits and breeders often use it to magnify interesting variations such as color morph, but is it likely to be deleterious to the health of the resulting beetles, similarly to how intensive in-breeding is inadvisable for mammals? Should I order from different suppliers for the initial batch, to ensure a varied gene pool at least starting out? Do sellers distinguish between captive-bred and wild-caught specimens, and should it matter to me which I get?


Also, do resulting eggs and larvae need to be removed from a common enclosure with adults to ensure survival? Is it cool to have individuals at different stages cohabitating? I imagine that even if the adults are herbivorous, they probably do practice some degree of cannibalism (either larvae eating each other, or larvae and adults eating eggs).


Do any of you have live plants in your beetle enclosures? I think this could be pretty attractive, and possibly enriching for the beetles (to whatever extent beetles can be enriched, I guess).

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Inbreeding isn't usually a problem with insects, but you could certainly get stock from different suppliers. Captive-bred/wild-caught shouldn't matter but you can ask a supplier which they are if it isn't specified.


I usually remove larvae and eggs when I notice larvae in the tank. It probably isn't necessary, but I have my beetles in a small tank so I remove larvae just to ensure that they have enough room to roam around and pupate. In a 5 or 10 gallon with deeper sub this would probably be unnecessary. Not sure about cannibalism although they are supposed to be pretty communal. At L3 the larvae seem fine together, but I have had a small group of L1 larvae turn into a very fat single L2 larvae. Not sure if that was an anomaly or not because one of the larvae was bigger than the others to begin with.


I have fake plants in my enclosure and the beetles don't seem to care much either way. They spend most of their time burrowing around, climbing a piece of cork bark, or stuffing their faces with food. :)

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Not to steal your thunder but I had a question as well about this species. How long does it usually take for larvae to mature?


The more the merrier, really! I was wondering that as well, and have heard 2-3 months.

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The more the merrier, really! I was wondering that as well, and have heard 2-3 months.


That sounds about right to me. I haven't kept track but all the L3 larvae I've gotten have pupated quickly, and my captive-bred larvae get bigger at a pretty rapid rate. I'll have to keep better track but depending on temperatures and whatnot your turnaround is probably a few months.

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