Oil Beetles

Perhaps it’s because there are so few blue plants, animals, or fungi in nature that they seem to really catch our attention. That is definitely true of this beautiful Oil Beetle (aka Short-winged Blister Beetle, Meloe angusticollis), photographed in eastern PEI earlier this month by Carla McKie.

Oil Beetles get their name from oily, orange droplets that ooze from their joints when the beetles are threatened. That substance is haemolymph (insect blood), and it also gives these creatures their ‘blister beetle’ name: the haemolymph contains a toxic chemical (cantharidin) that causes painful blisters on anyone unwise enough to touch it.

Despite these unpleasant effects, cantharidin has been taken internally for thousands of years as everything from an aphrodisiac (you may know it as ‘Spanish Fly’) to a treatment for rabies, tuberculosis, and cancer. Today, canthardin is used externally as a treatment for warts and viral skin infections, and research is ongoing into other potential uses.

Cool biochemistry is only one of the Oil Beetle’s interesting features; these insects also have an unusual life cycle. Meloe angusticollis mates and lays eggs in the soil in spring. Within a few weeks, those eggs hatch into larvae, called ‘triungulins’ that climb onto nearby flowers and wait for ground-nesting Mining Bees (Andrena sp.) to come by.

The larvae latch onto a female bee, and she unknowingly transports them back to her nest. Once there, the larvae feed on the bee’s eggs and food cache, mature through several stages (instars), and overwinter, before pupating and emerging as adult Oil Beetles in spring.

Now, back to that unusual colour: Oil Beetles’ hue isn’t due to pigmentation, but rather to the way their exoskeletons reflect light. As a result, Oil Beetles can look vivid blue in some lighting and dull black in others. Regardless of colour, Oil Beetles’ body shape, short wing-covers (resembling a waistcoat), and knobby antennae are helpful identifiers. This individual’s antennae tell us it’s a male; females’ antennae lack that prominent bend.

Although we humans have an anti-parasite bias, Oil Beetles don’t harm Mining Bee populations and are actually indicators of a healthy ecosystem. Oil Beetles are native and truly fascinating parts of PEI Untamed!