Eastern gray squirrels are frequent visitors to our backyard bird feeders here in central Florida. One day in early August, a squirrel appeared full of what I thought were cancerous growths on its body. The growths were large, dangling enlargements that protruded an inch or so from the pelt of the squirrel. Despite its “diseased” state, the squirrel seemed healthy and spry.
After a little research I discovered something quite gross – a good news, bad news outcome. No, it was not cancer, but with bot fly larvae. The bot fly is a bumblebee-like looking fly that uses the squirrel to host its larvae.
The adult fly lays eggs on the twigs and branches of the vegetation that squirrels live in and when larvae hatches, they attach themselves to the squirrel that brushes up against them. The larvae enter the squirrel via the mouth, nose and anus where they find their way to the sub-cutaneous tissue of the animal. Once in the skin, the larvae make a hole in the skin called a warble and align themselves with their heads buried in the squirrel and abdomen at the skin’s surface where excrement is passed. The last thing a bot fly wants to do is to kill its host so it sucks just the lymph fluid, not the blood, for nourishment and does not damage the muscle or other important tissues.After four weeks, the larvae falls to the ground where it burrows into the soil and pupate to undergo metamorphosis. It emerges as an adult bot fly to start the cycle over again.
The squirrel usually survives and the warbles heal over time unless it is inundated with too many warbles. I only saw this squirrel a couple of times at the feeder and hope that it did fine once the bot fly larvae dropped from it. It makes me think twice before bushwhacking through brush to capture pictures. That is for sure!