Diet composition and prey selection of Cordulegaster maculata Sel. larvae (Anisoptera: Cordulegasteridae)

The larvae of Cordulegaster are generally found in the pools of streams where they lie in ambush, buried in the substrate, awaiting unsuspecting prey. J.G. NEEDHAM & H.B. HEYWOOD (1929, A handbook of the dragonflies of North America, Thomas, Springfield) suggest that they prefer largeprey such as subyearling brook trout ( (Salvelinus fontinalis) which may be as large as the larva itself. During September of 1980 C. maculata larvae were collected from Trucka Brook in Essex County. New York. Trucka Brook, a small low gradient stream with sand, gravel and muck bottom is located in the central Adirondack Mountains. On the day collections were made, water temperatures ranged from 8.0 to 11 5°C. A total of 62 larvae were collected in 12 standard Surber collections. Six samples were taken at 06,00 hours EST on 20-IX-80 and six more at 18,00 hours EST on the same date in order to represent both nocturnal and diurnal feeding by the larvae. The Surbers samples were preserved in 5% formalin in the field and later were sorted, identified and stored in 70% isopropanol. The contribution of each invertebrate taxa in the environment (Surber samples) and in the diet of C. maculata was determined on a percentage dry weight basis. Larval anisopterans were identified using the keys of NEEDHAM & HEYWOOD (cf. above) and J.G. NEEDHAM & M.J. WESTFALL(1955, A manual of the dragonflies of North America, Univ. California Press, Berkeley).