Saturday, February 09, 2008

Maple Eyespot Gall

Back in 2001 while attending an Earthwatch expedition I came across a maple leaf that was obviously different from a normal maple leaf, having small bull's eyes covering a good portion of it. It was very pleasing to the eye. At the time I had no idea that I had come across an insect gall- Eyespot maple gall to be exact. A gall is actually the result of a reaction by a plant to irritaion caused by an egg-laying parasite in the form of an insect (e.g. flies, wasps, aphids, mites, and midges). Other types of galls can also be caused by nematodes, bacteria, viruses, and fungi. This reaction actually plays in favor of the parasite causing the plant's tissues to grow around it forming a "shelter" for its development. Harm to the plant is usually minor, though there are some that do cause severe damage. The parasite responsible for this particular gall is the maggot larvae of the ocellate (or maple eyespot) gall midge. The bull's eye is formed by substances secreted by these maggots. Once they mature they'll drop to the ground below and burrow into the soil where they'll eventually rise as adults. Galls can be fuzzy, smooth, spiny and can come in a variety of shapes and sizes as seen by another example in the photo below.

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