THE HALOBATES 



INTRODUCTION 



The only truly pelagic insects known belong to the 

 genus Halobates placed in the family Gerridae, subfam- 

 ily Halobatinae. Like all their congenors they are gre- 

 garious, adapted to skim very rapidly over the surface 

 of the water, and are carnivorous, feeding on both liv- 

 ing and dead animals. 



Over twenty species of the genus have been de- 

 scribed. Some of them, such as H. micans Esch. and H. 

 sericeus Esch., are widely spread oceanic forms where 

 as most of the others, according to the records, occur 

 not far from land areas or are restricted to definite 

 seas or oceanic coastal regions or small bodies and 

 streams of salt water. Apparently they are rarely or 

 never found in fresh water. The best single account of 

 this group is that of F. Buchanan White in "The report 

 on the pelagic Hemiptera procured during the voyage of 

 H.M.S. ChaUenger in the years 1873-1876," published in 

 1883. Besides a detailed description with figures of the 

 ten known species, considerable space is devoted to a 

 general consideration of their structure with a few ob- 

 servations on their habits and geographical distribution. 

 Since the publication of this report, the number of spe- 

 cies has been more than doubled and considerable added 

 to our knowledge of their habits and life history by var- 

 ious scientists, notably William Lundbeck (1914), H. C. 

 Delsman (1926), Fred C. Hadden (1931), and G. M. Henry 

 (1932). 



The genus Halobates was established in 1822 by J. 

 Friederich Eschscholtz in Entomographien I, p. 106. A 

 rather free translation of the salient factors of his char- 

 acterization is as follows: The head is broad. Eyes 

 large. Ocelli missing. Rostrum three-jointed. The 

 four -jointed antennae attached before the eyes; first 

 joint the longest. Pronotum very short, ring-formed. 

 Apterous. Abdomen very short. Fore legs very short, 

 with thickened femora; the tibiae cylindrical and equal to 

 the femora in length, provided inwardly with a project- 

 ing hook-like process; the tarsi composed of two rather 

 long, thick joints; the second joint provided with two 

 curved hooks. Middle legs two or three times as long as 

 the body; femora very long, cylindrical; tibiae thinner 

 and about one-half the length of femora; tarsi two- 

 jointed, the first segment a little shorter than tibiae and 

 usually bent, the apical joint short, fine, and provided 

 with several long hairs. Hind legs joined to the body 

 above the middle legs, about one-third shorter than the 



latter, with longer coxal joints; finer tibiae and tarsi; 

 the second joint of the latter is acutely pointed and long 

 haired. The body is covered with very fine silver - 

 colored scales. The legs are usually black. These ani- 

 mals leap over the surface of the ocean and live only in 

 or near the tropics. 



For distinguishing the various species the chief 

 characters in use are the size of the anterior femora, 

 the relative lengths of the segments of the antennae, of 

 the legs, and particularly of the tarsal segments, as well 

 as the character of the male genital segment. In sever- 

 al species the shape of the body, as well as the color, is 

 quite characteristic. 



One hundred and thirty-six specimens of Halobates 

 were collected on the voyage of the Carnegie. Of these, 

 seventy-six were adults and sixty were nymphs or 

 nymphal skins. Only three species are represented: H. 

 micans Esch. (=wullerstorffi Frauen.), H. sericeus 

 Esch., and H. splendens Witl. The first two of these are 

 the most common and widely distributed pelagic species 

 of the genus. 



KEY TO THE THREE SPECIES OF HALOBATES 



1. Fore femora and antennae black, never steel blue. 



Second and third segments of antennae together sub- 

 equal to fourth, third segment but little if any 

 longer than second. Anterior tarsus with the ter- 

 minal segment about twice as long as basal; tarsus 

 of intermediate legs with the basal segment about 

 seven times as long as terminal; tarsus of hind 

 legs with terminal segment one-third as long as 



basal sericeus Esch. 



Fore femora, antennae in part, and often the other 

 legs steel blue. Terminal segment of fore tarsus 

 not twice as long as basal 2 



2. Anterior tarsus with the terminal segment one-fourth 



to one-fifth longer than basal. Tarsus of intermedi- 

 ate legs with the basal segment 4 to 5 times as long 

 as the terminal one; posterior femur one-third to 



one-fourth longer than tibia micans Esch. 



Anterior tarsus with the two segments subequal. Tar- 

 sus of intermediate legs with the basal segment 6 to 

 7 times as long as the terminal one; posterior femur 

 one-eighth longer than tibia splendens Witl. 



DISCUSSION 



Halobates sericeus Eschscholtz 

 Figure 1 (A) 



Body not at all parallel sided; ovate, widest across 

 the middle of the mesonotum. Color ash-gray or prui- 

 nose above and below, with anterior ventral segments 

 often embrowned; legs and antennae black, never steel 

 blue. Antennae two-fifths shorter than body; first seg- 

 ment not nearly twice as long as second but plainly long- 

 er than second and third united; third segment nearly 

 equal to second and much shorter than fourth. Anterior 

 femur about one-sixth longer than tibia and the latter 



two-fifths longer than tarsus. Anterior femur, seen 

 from the side, at the widest point, about one-fourth as 

 wide as long; the basal segment of the anterior tarsus 

 one-half the length of the terminal one. Intermediate 

 legs with the femur twice as long as the tibia, and the 

 latter subequal to the tarsus in length; basal segment of 

 the tarsus 6 to 7 times as long as the terminal. Poste- 

 rior legs with femur over one-third longer than tibia, 

 the latter just over three times as long as tarsus. 

 Length 3 mm, diameter 1.75 to 2 mm. 



Most of the specimens taken in the Pacific Ocean 

 belong to this widely spread species. The numerous 



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