THE HOVERFLY BODY

Body parts: the first, second and third segments and the arista (implanted on the third A hoverfly’s body consists of a head, a segment). The first two segments are gen- thorax and an abdomen (figure 6). This erally small, the third is large. The arista is section provides descriptions and names hair-like. Two moon-like structures are for the main structural features associated visible just above the antennae, these are with these body parts. the lunula. The frons is the area between the lunula and the compound eyes. On top of the head near the thorax lie three antenna slightly raised ocelli. Below the antennae, leg 1 most species have a facial knob, which is head humerus most obvious when viewed side on. thoracic dorsum Below the facial knob is the mouth edge, visible as a rim in most species. In a lim- thorax ited number of species the mouth edge postalar knob forms a long snout, for example, in

scutellum Rhingia. The area below both compound halter eyes is called the genae. This can be a tergite 2 small strip, as in most species, or it may be leg 2 wider. abdomen vertex tergite 3 ocelli compound eye leg 3 frons frons tergite 4 lunula

hypopygium antenna arista figure 6. Basic body parts of a hoverfly.

facial knob Head

mouth edge Much of the head (figure 7) is occupied by the compound eyes, which are usually genae brownish or reddish in colour. In females, figure 7. Structural features of a hoverfly the compound eyes are separated by a head. wide gap (dichoptic), while in most males the eyes meet on the upper side of the head (holoptic). This makes the com- Thorax pound eyes a useful characteristic for dis- tinguishing males from females in the Viewed from above, the thorax consists of field. In some genera the males’ eyes are the thoracic dorsum and behind that, the also separate, for example, in Microdon, semi-circular scutellum (figure 6). The legs Neoascia and Helophilus. Males can then be and wings are attached to the thorax. The recognised by the globular genitalia at the thoracic dorsum may display colour pat- tip of the abdomen. terns, such as white stripes or yellow spots. Two antennae are embedded on the front The sides of the thorax consist of many dif- of the head. The antennae consist of four ferent parts (figure 8). The presence of hairs

21 3

2 1

4 5 20

7

8 6

17 18 16

15 9

14

12 10

11

13

19

figure 8. Structural features of the sides of the thorax. Numbers correspond to those listed in table 1.

Table 1. Body parts of the sides of thorax.

Number Name used in Alternative Dutch name in figure 8 this book (Van der Goot, 1981)

1 humerus postpronotal lobe schouderknobbel 2 notopleuron 3 suture dwarsnaad 4 postalar knob postalar callus achterhoeksknobbel 5 anterior anepisternum anterior mesopleuron voorste vlakke deel middenzijplaat 6 posterior anepisternum posterior mesopleuron middenzijplaat 7 proepisternum 8 proepimeron 9 coxa 1 10 katepisternum sternopleuron borstzijplaat 11 coxa 2 12 meron hypopleuron onderzijplaat 13 coxa 3 14 metepimeron 15 katepimeron 16 katatergite metapleuron achterzijplaat 17 anterior anepimeron pteropleuron vleugelzijplaat 18 posterior anepimeron 19 metasternum (below, between coxa 2 and 3) 20 scutellum

22