Poisonous Blood

Since adult fireflies advertise their presence by flashing in the dark, and their larvae also glow when disturbed, they would seem to be an easy target for predators. Bats, toads, and spiders can all spot a firefly's illumination. However, fireflies and their larvae are not as defenseless as they might appear.

Reflex Bleeding

When attacked by a predator, some fireflies shed drops of blood (hemolymph) in a process called "reflex bleeding." The blood contains a chemical that is distasteful and even toxic to many predators.

Studies have shown that predators soon learn to steer clear of fireflies. Some also shun perfectly palatable insects that have been painted with a glowing substance to resemble a firefly larva.

The predatory Photuris fireflies are not able to make this defensive chemical on their own, but they can gain the poison, and thus the protection, from the fireflies they eat. The poison is then passed on to their eggs and resulting larvae.

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Fireflies can't see blue light, so you can safely observe them using a blue flashlight.

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