Red maple, Acer rubrum, is a magnificent native North American tree renowned for its dashing green summertime leaves and gorgeous autumn foliage. Last week, while gazing at the foliage of a red maple, I was surprised to see the maple leaves looking back at me. Unblinking vacuous eyespots ringed with orange and bright red stared from the top of a maple tree across the forest. What strange twist of vegetal trickery was this?
A closer inspection revealed the presence of a small sessile maggot hiding just beneath the surface of the leaf, dead center in the eyespot. The maggot was the larva of the ocellate gall midge, a small fly adapted to complete its life cycle by consuming tissue of the red maple. The story of the gall midge began several weeks ago, when these tiny mosquito-like flies emerged from pupal cases that survived the rigors of winter in the soil beneath the maple tree. These small midges are close kin to the boxwood leafminers we met on April 30, 2012 in the episode entitled “Twisting the day away.” After escaping their terrestrial internment, males and females mate, and then females fly to the canopy of a maple tree, where they deposit eggs in the soft tissue on the underside of the young leaf. Upon hatching, each larva, a.k.a. maggot, attaches itself to the leaf with its mouthparts and secretes potent hormone-like chemicals that co-opt the normal development of the leaf.
As the larva grows, it induces the leaf to develop a slight swelling directly above its location. This abnormal growth is technically known as a gall. In addition to inducing a gall in which it feeds, the larva causes the leaf to develop striking concentric rings of yellow (carotenoids) and red (anthocyanins) pigments not usually seen until the glory days of autumn. After a few weeks of dining on nutritious tissues within the gall, the larva drops to the earth and forms a pupa in which it spends the remainder of summer, autumn, winter, and early spring, before completing its metamorphosis and emerging as a small fly next spring. So, as you wander the waysides keep an eye on the maples - they may just be looking back at you!
Bug of the Week thanks the eagle-eyed Dr. Shrewsbury for providing the inspiration for this episode. The delightful reference “INSECTS THAT FEED ON TREES AND SHRUBS” by Warren Johnson and Howard Lyon, and “ACERICECIS GAGNE, A NEW GENUS FOR CECIDOMYIA OCELLARIS OSTEN SACKEN (DIPTERA: CECIDOMYIIDAE), THE MAPLE LEAF OCELLATE GALL MAKER IN NORTH AMERICA” by Raymond J. Gagne were consulted in preparation for this article.
For more information on maple eyespot gall, please visit the following website: