Raising Bumble Flower Beetles

The Bumble Flower beetle (Euphoria inda) is a small, fuzzy, mottled brown beetle native to North America. They can be found across most states, but are most commonly found along the Eastern seaboard and Midwest of the United States. In nature, this diurnal species of beetle buzzes among flowers during the warm summer months to eat nectar and pollen, making them an important pollinator, and can easily be mistaken for a bumble bee at a glance. While normally the mottled brown pattern, they can also uncommonly be all-black in coloration. At the time of writing it is unknown if this is an inheritable trait, but with luck this will be discovered next year.

They are an intermediate experience species to raise, possessing a short larval period and comparatively long active adult lifespan. However, they have a very seasonal breeding pattern requiring cold hibernation as adults. This is not meant to be an exhaustive guide on every possible way to care for these animals, but reflects our personal experience. Better methods may be discovered as more generations are raised in captivity.

Basic care:

For adults:

Optimal temperatures: 72-80F/22-27C
Optimal humidity: 60-70%

Adult beetles can be kept in enclosed terrariums at least roughly ten times the length of the beetle in any given dimension, or larger. More space is better, but small terrariums are just fine. For small groups of 2-6 beetles, small jumping spider enclosures work great.

These beetles can be kept together communally and don’t seem to fight each other. They should be kept in loose, soft substrate that is at least two centimeters deep, as they often dig to hide when not exploring or feeding. Coco coir makes for a great substrate as it retains moisture well, will not scuff up and wear down exoskeleton as easily as soil, and resists mold. Sticks, leaves, and bark pieces should be placed on the surface of the substrate to give the beetles something to climb on and aid them in flipping over if they end up on their backs. A secure lid is required, as these beetles are very adept fliers and are attracted to sunlight. Metal mesh is fine, but not optimal, as it can wear down their claws faster than normal. The enclosure should be misted regularly to maintain humidity. The enclosure can be placed near windows for indirect sunlight, but may get too warm in direct sunlight. Conditions outside the optimal ranges can adversely affect lifespan in adults and can risk them not surviving overwinter to breed in the spring.

Adults are nectar and pollen feeders, but will eat soft, sweet, ripe fruits in captivity. Banana, and cantaloupe are readily accepted, as is cotton soaked in a simple 1:2 solution of white sugar to water. They do not show much interest in beetle jelly.

Adult beetles, after eclosing and emerging in early summer, will remain active, digging, exploring, and eating to store energy until the fall. Breeding behavior has been seen during the summer months, in captivity there may be potential for two broods in a year, but it has not been confirmed yet. Around September/October, adults will become less interested in food, and will start to stay buried in an effort to find a good place to hibernate through the winter. At this point, adults can be transferred to a smaller container filled with breeding box substrate (see below), and kept around 50F/10C as a way to simulate colder winter temperatures. Wine coolers, small refrigerators with a temperature controller, or even an enclosed porch if it doesn’t reach freezing temperatures can potentially suffice. In the spring, around early March, the container of hibernating beetles can be brought back to room temperatures as the beetles will start becoming active again to breed, lay eggs, and die shortly after. Breeding may have also occurred during the summer.

For larvae:

Optimal temperatures: 68-75F/20-24C
Optimal humidity: 60-70%

After hatching, larvae develop and gain weight through three separate stages before finally pupating, known as instars; normally referred to as L1, L2, and L3. In optimal conditions, a larva will typically spend about 1-2 weeks each at L1 and L2, and 2-3 months at L3. Taking care of larvae is simple as your goal is to provide them with enough substrate and moisture to grow while disturbing them as little as possible.

The larvae feed on decayed wood, compost, and rotten leaves. They can be kept on pure flake soil, or a mix of organic compost, decayed leaves, and flake soil. Flake soil an artificially decayed substrate made from sawdust and wood flakes, this can be purchased online, or made at home in 2-4 months. Check our resource on making your own!

The prepared substrate should hold it’s shape when compressed in your hand without dripping water.

A normal terrarium setup isn’t going to be the best method for keeping larvae. Lidded deli/food containers are perfect. Some ventilation holes are needed, 12-24 pinholes in the lid will suffice. The entire larval period for a single grub can be maintained in a 5oz deli cup filled with their substrate. Multiple larvae can be kept together in larger containers, say 5-8 in a 24oz tub.

The idea is to keep them in a size of container that will hold enough for the larva to eat in a single month. They are voracious for their size, and can go through up to 15-20oz of substrate (by volume) during their larval forms. Replace spent substrate when the surface is mostly frass. Ideally, some of the remaining soil should be retained and mixed in with the fresh flake as it contains beneficial bacteria and will reduce the potential for shock to the larva from any PH differences between the spent and fresh substrate. Occasionally spraying the surface of the can help keep the substrate moist if it dries out some between changes.

After 2-3 months at L3, the larva will begin to look more yellow and start to shrink. This indicates that they are getting ready to pupate. They will form a hollow, egg-shaped chamber typically toward the bottom of the container as a pupal cell. Sometimes you may get lucky and have a small window on the bottom of the container to observe if they have pupated. The larva will lose weight and become wrinkly as it uses fluid stored in its hindgut to line and smooth the chamber. At this point you should not replace the substrate and the best course of action is to just leave them completely alone so you do not accidentally break their cell. If you cannot see the larva from the outside, dig slowly and carefully if you are doing maintenance, if you start finding an oval area that seems tough or hard packed, that is likely a pupal chamber.

For Pupae:

After constructing a cell, the larva will lose all mobility and pupate. This is when the beetle is the most vulnerable and fragile. If you’ve found an intact pupal cell, the best course of action is to leave it completely alone. Intact cells can also be collected and kept in a container on damp paper towels if you want to keep an observation on emerging adults.

A broken cell is unfortunately often fatal, as flower beetles do not often survive well in artificial cells, though you can always try if you’ve found yourself in that situation.

A small block of damp wet floral foam can have an oval shape pressed into it not be much larger than the pupa itself; the pupal cells of flower beetles are quite tight-fitting. Gently roll the pupa into the hollow and leave them be. The success rate using this method is low, maybe 25-50% survive and become adults. Any damage to the pupa, even a minor crack or dent will be fatal.

After 2-3 weeks, adult beetles will eclose and start emerging. These emerged beetles are active and ready to be placed in a suitable enclosure with food, though they may not eat right away.

Breeding:

Lacking showy horns or mandibles for sparring like rhinos, stags, or larger flower beetle species, it can be difficult to properly sex adult E. inda without close observation. The easiest method is to examine their antennae. The clubbed, lamellate tips are longer on males compared to females. Females are also more often larger-bodied overall, but that’s not a perfect method to use.

Bumble flower beetles seem to be very seasonal when it comes to breeding. They are active upon emerging as adults in early summer to gorge on nectar and sugars to store energy for hibernation, seek shelter in the fall, remain dormant overwinter, and re-emerge in spring to look for mates and reproduce. A single adult female beetle can lay upwards of 100 eggs if a suitable location is provided for her to do so. Males and females can be overwintered together, and if they survive hibernation, may have already mated before you know they are active again. For this reason, it is recommended that beetles are placed in laybox substrate when put away for cold storage during the winter.

Laybox Preparation:

Optimal temperatures: 68-75F/20-24C
Optimal humidity: 60-70%

Choose a large container with a secure lid – plastic totes or bins work well. A 19Qt/18L storage bin or larger is recommended. Add ventilation holes. For the egg laying medium mix together roughly 25% flake soil, 25% organic compost soil (no additives like fertilizer, perlite, or definitely pesticides!), and 50% crushed/mulched decayed leaves. Try to collect decayed leaves of maple, beech, and oak trees from the previous years’ fall, not freshly fallen leaves. Leaves should be baked in the oven at 250F/120C for about half an hour to sterilize before adding. This substrate should be hydrated enough to hold its shape when compressed without crumbling.

The bins should be filled at least half way with loose substrate. There is no need to pack or compress the substrate.

You can add bark, sticks, and food just like their summer enclosure, but egg-laying adults may not eat. Multiple females and male beetles can be put in together, ideally at least one male for every five females for the best chances of successful breeding, upward of 12-18 beetles per bin. From there, leave it in a place where it won’t be disturbed, but will still get some natural light in case that’s beneficial.

Egg Collection:

Once you have a laybox prepared, it’s up to you for how you want to handle any eggs potentially being laid. You can simply leave the bin alone for a few weeks, changing the food as needed if it’s starting to spoil. Adult beetles will usually die during or shortly after the egg-laying process. After a few weeks, you can sift through the substrate to collect eggs and any hatched larvae.

Eggs are tiny and pearly-white, between 0.5-1mm, and can be gently handled without breaking. Eggs can be moved to individual cups of moist flake soil or laybox substrate, but given the number of eggs produced, it’s often easier to simply add eggs to hollows in a container of substrate to monitor until they hatch.

Eggs will develop over the course of 1-2 weeks as they expand and absorb moisture before hatching. Fresh L1 larvae will often eat their egg shell while their head capsule hardens to a brown color, and dig down into the flake soil after a day or two. From here, refer to the larval care section above! Congrats!