Interactions between the dragonfly Hagenius brevistylus Sel. and the damselfly Calopteryx maculata (P. de Beauv.) (Anisoptera: Gomphidae; Zygoptera: Calopterygidae)

Observations during the summer of 1984 revealed that the gomphid dragonfly Hagenius brevistylus is not only a significant predator of Calopteryx maculata but that its mere presence may interfere with feeding, mating, and thermoregulatory behavior of the damselfly. The interactions were noted while I was observing the feeding behavior of female C. maculata on Moore Creek, a tributary of the New River in southwest Virginia. On five occasions during the summer of 1984 H. brevistylus was observed capturing and consuming C. maculata. Three females and two males of the latter species were captured. Of particular interest were the interactions observed on July 9. At 09.27 h I had begun recording the feeding behavior of four female C. maculata in a streamside aggregation. This species captures very small flying insects on short flights, usually less than a meter from the perch. Females often retain the same feeding perch for several hours, and in some instances return to the same perch on successive days. All females in the aggregation were feeding regularly and exhibiting the characteristic wingclapping behavior between each feeding flight. At 09.55 h H. brevistylus flew into the vegetation among these perched females, and it adopted a cryptic head-up tail-down posture on a stem approximately one-half meter above the stream bank. Significantly, all C, maculata in the immediate area ceased feeding and wingclapping. H. brevistylus remained motionless as did all of the female C. maculata. At 10.14 h a new female C. maculata entered the area and began feeding flights about 1.5 m from H. brevistylus. On,the third feeding flight H. brevistylus attacked her but missed. The escapee then remained on a perch and neither fed nor wingclapped. At 10.34 h another C. maculata arrived and was immediately captured by H. brevistylus. The captured individual was carried to a blackberry cane above the stream and was consumed over a period of 25 minutes. All C. maculata in the area continued to remain motionless. At 11:08 h a third female C. maculata arrived in the area and began to feed and wingclap. This individual too was captured by the H. brevistylus and consumed on the branch of a small locust tree. (On all occasions on which H. brevislylus was observed feeding on prey, it was perched on a thorny branch, such as that of blackberry, wild rose, or locust).