The middle step in the fly lineup. “Spikes” is the feeder-world name for fly pupae: small, hard, reddish-brown capsules that look like grains of rice. These are the pupae of the green bottle fly, Lucilia sericata, and they hatch into flies a touch smaller than blue bottles (8–10 mm vs 12–15 mm), the right step up from fruit flies for L5–L6 mantises and smaller reptiles.
If you’ve ever watched a growing mantis ignore fruit flies it has clearly outgrown, this is the feeder that fixes it. Pupae don’t eat or need care, so you hatch flies on your own schedule. The full method is in the hatch guide; it works the same for green and blue bottles.
The Feeder Size Ladder
Match prey size to your animal’s stage. Green bottles sit right in the middle:
- D. melanogaster (≈2 mm): L1–L2 mantis nymphs, spider slings, froglets.
- D. hydei (≈3 mm): L3–L5 nymphs and small predators.
- Green bottle flies (8–10 mm): L5–L6 mantises and smaller reptiles.
- Blue bottle flies (12–15 mm): L6+ and adult mantises, chameleons, larger reptiles.
A good rule of thumb: prey no more than a third of the mantis’s body length. When in doubt, size down. A mantis will happily take two smaller flies, but an oversized one can be refused.
How to Hatch and Feed Them
Put the spikes you want to hatch in a ventilated cup (pinholes or a mesh lid, never sealed) somewhere 70–80 °F. No food, water or bedding: pupae don’t eat. Flies usually emerge in 2 to 7 days, faster when warm, slower when cool, and they stall below about 65 °F.
Unlike fruit flies, bottle flies can fly. Keep the lid on once they emerge. Before feeding, chill the cup in the fridge for 5–10 minutes so the flies go sluggish, then tip a few into the enclosure. A dab of honey or sugar water in the fly cup keeps the adults lively for the week or two they last. For reptiles and frogs, follow your species’ own supplement schedule; mantises don’t need dusting.
Storage & Shelf Life
Not ready for flies yet? Refrigerate the spikes at about 40 °F (the crisper drawer is ideal). Plan on about a week, sometimes closer to two, and use them while they’re fresh, since fewer hatch the longer they sit. Never freeze them: the freezer kills pupae. Take out what you want to hatch and put the rest back in the cold.
Frequently Asked Questions
What are green bottle spikes?
Green bottle spikes are the live pupae of the green bottle fly, Lucilia sericata. They look like hard, reddish-brown grains of rice and hatch into 8–10 mm flies at room temperature, bigger than fruit flies and smaller than blue bottles, ideal for L5–L6 mantises and smaller reptiles.
Are green bottle flies the right size for my mantis?
They suit L5–L6 mantises. Nymphs through L4 should be on fruit flies; from L6 and as adults, move up to blue bottle spikes. Prey should be no more than a third of the mantis’s body length, so size down if unsure.
How long do fly spikes last?
In the fridge at about 40 °F, around a week, sometimes closer to two, with fewer hatching the longer they wait. At room temperature they hatch in 2 to 7 days, and the adult flies live a week or two.
Do I need to dust the flies with calcium?
Not for a mantis; dusting is for frogs and reptiles. If your animal needs supplements, drop the flies into a cup with a light pinch of powder, swirl gently and offer. See the feeding guide for how we feed mantises.
