May, 1901.] 



KNOWLEDGE. 



115 



occiirriug below high-water mark. These have iuvaded 

 tlie tidal aiea not from the frcshwators, but from the 

 h»nd. Most, sea-shore beetles, indeed, are iuciusoi-s from 

 the laud. Many beetles of various families abound in 

 salt-marshes and on coast sand-dunes ; certain kinds 

 can be traced down to high-water mark, whilst the most 

 characteristic beetles of the sea dwell between tide-marks 

 and undergo immersion twice every day. 



In temperate countries at least, the Rove-beetles 

 (Staphylinidae) form the most numerous family of the 

 order, and on the soa^shore they maiut^ain this pre- 

 dominance. The form of these beetles is generally 

 known. They are usually narrow, elongate insects, with 

 very short wing-cases, beneath which the membranous 

 hind-wings are nevertheless completely folded up and 

 hidden when at rest. The hind-body, not as in most 

 beetles, covered by the wing-cases, but projecting far 

 beyond them, has all its seven segments firm-skinned and 

 freely movable, so that this part of the insect can be 

 turned about at pleasure ; a number of Rove-beetles 

 carry it turned upwards, as a scorpion carries its tail. Most 

 of the Rove-beetles prey upon insects smaller or 

 weaker than themselves. 



Many salt-marsh and sand-haunting Rove-beetles 

 belong to the large genus Bledius, which, with some 

 allies, differs from most genera of the family by the feet 

 having only three (instead of five) segments. The Bledii 

 dig bui-rows in the sand or mud, and the material they 

 throw up forms little heaps or castings. Several species 

 live on sandy sea-coasts. The habits of B. fuscipes, Rye, 

 were observed with some care years ago by Mr. K. 

 Taylor ; these insects seem to live amicably in pairs. 

 At the bottom of a vertical bui-row about an inch and 

 a half deeji, one individual — presumably the female — 

 was found, while her mate mounted guard in a short 

 horizontal tunnel opening out from the burrow near the 

 surface of the sand. 



Xearly allied to the Bledii, and of somewhat similar 

 habits, are the smaller, more hairy and less spiny beetles 

 of the genus Trogophloeus. These arc often found in 

 marshy places by the banks of streams. A new marine 

 species, T. anglicanus, which has lately been described by 

 Dr. Sharp from specimens discovered near Plymouth, is 

 of uncommon interest, since it seems to be almost 

 idantical with a beetle (T. unicolor, Fauvel) of similar 

 habits that lives on the coast of New Zealand. M. 

 Fauvel, indeed, does not consider that the slight struc- 

 tural differences wairant specific seiparation. In his 

 record of the discovery. Dr. Sharpt discusses the problem 

 of this strange similarity, and considers that the only 

 alternative to the highly unlikely suggestion that the 

 insect has been brought by ships fi'om the other side of 

 the world, is that closely similar species have been inde- 

 pendently developed here and at the Antipodes, under 

 similar conditions of life. The possibility of a multiple 

 origin for the same kind of animal in different localities 

 can hardly be denied, since it is certain that the same 

 variety can be thus independently produced under similar 

 conditions, and what is a variety but a species in process 

 of being made? 



Quite a number of Rove-beetles may be found running 

 among the decaying seaweed that is cast up by the high 

 tides. Several of the large and widely-spread genera of 

 these insects have each two or three species living in 

 this way. The genus Aleochara for example (charac- 

 terised by the presence of an extra tiny segment on each 



+ D. Sliarp. " Some undescribed Species of Trogophloeus." Ent, 

 Mo. Mag. XXXVI., 1900, pp. 230-4. 



palp or jaw-foot) has three seaweed-haunting species 

 widely distributed around our coasts. These are> charac- 

 terised by their dull blackish bodies, having a thick 



whitish hairy clothini;. Such a covering is very often 



"... ® ." 



found on marine insects ; its use to them is evident, as 



it serves to retain a layer of air around them when they 



undergo immersion. Even when covered by water they 



are not really wetted. 



Similarly the largo allied genus of Homalota has a 

 small group of marine species. In their general aspect, 

 the pale hairy clothing, the relatively short feelers, and 

 the parallel sides of the hind-body, these Homalota; arc 

 remarkably like the Aleocharse just mentioned. By some 

 authorities, therefore, the two groups of beetles are 

 believed to be closely allied. But the minute stinictural 

 differences between them — the number of segments of the 

 palps and of the fore-feet for example — seem to show 

 that their likeness to each other is the result of a con- 

 vergence under similar conditions of life. J 



Belonging to the same group of the Rove-beetles as the 

 Homalots are some small insects belonging to the genus 

 Myniiecopora (or Xcnusa), altogether adapted to a sea- 

 shore life, only being found close to the water's edge, 

 ciud often occurring between tide-marks. Two kinds — 

 M . uvida, Er., and M. sulcata, Kies., inhabit our shores. 

 These little insects may be seen either running briskly 

 among the seaweed and on the rocks and shingle, or 

 flying quickly in the sunshine. Sometimes they may 

 be observed to alight on the water of a rock-pool, then, 

 their expanded wings serving as sails, they are easily 

 blown along on the surface-lilni. 



Both the Aleocharje and the Homalotae are small 

 insects — only about 3 mm. (J- inch) in length. There are, 

 however, some more imposing Rove-beetles found among 

 seaweed, measuring from 5 to 12 mm. (4 to ^ inch). 

 These are the species of Cafius, all of which seem to 

 inhabit the sea-shore, or at least the mai-gins of tidal 

 livers; they are nearly related to the beetles of the 

 large and dominant genus Philontlius. We have four 

 species on the British coasts — C cicatricoms, Er., C. 



Fig. 1. Fig. 2. Fig. .3. 



FlO. 1. — Actocharis Readingii, uiagniBed 15 times. 

 Fig. 2. — Grub of Cafius, magnified 4 times. 

 Fig. .3. — Cafius fucicola, magnified 4 times. 



fucicola, Curtis (Fig. 3), C. xantholoma, Grav., and C. 

 sericeu.?, Holme. The first of these seems confined to the 

 south coast; all the others are widespread, but only 

 C. xanfholoma can be considered common. C. sericeus 

 IS the only species of Cafius which has the woolly covering 

 usually characteristic of marine insects. As one turns 



JW. W. Fowler. "The Colcoptcra of the British Islands." 

 London, 1887-91. L. Granglbauer. " Die Kafer von Mittelcuropas," 

 Wicn, 1892, etc. 



