112 
Guide to A rachnida. 
Table-case 
No. 26. 
Fam. — Trombidiiclae. 
The Trombidiidae are soft-skinned mites, the palpi are free, 
the penultimate (or, more rarely, the last) segment being armed 
with a claw. 
Most of the mites of this family are free-living forms, which 
are either predatory or herbivorous. A few species are parasitic 
upon vertebrates and insects. The species of Trombidium are 
clothed with long, red, velvety hair, and present a striking appear- 
ance. The European representatives of the genus are of small 
size ; in the tropics, however, large species, measuring about half 
an inch in length, occur. The harvest-bugs, which cause irritation 
in autumn by burrowing under the skin, are six-legged larvae 
belonging to various species of Trombidiidae. The spinning-mites 
( Tetranychinae ), which occur in immense numbers on various 
kinds of plants, cause much damage to vegetation. They spin a 
fine web, which is usually found coating the lower side of leaves. 
The bright glaze, which may sometimes be seen on the trunk 
and branches of the lime tree, is produced by one of these mites 
{Tetr any elms telarius). 
Fam. — Hydrachnidae. 
The Hydrachnidae, or water-mites, resemble the Trombidiidae 
closely in structure. The legs are furnished with swimming- 
hairs. 
Most of the Hydrachnidae live in fresh water, but there are a 
few marine species. Their food consists of small Crustacea, insect 
larvae, infusoria, etc. They are widely distributed and there are 
numerous British species. 
F am . — Halacaridae . 
In the Halacaridae the buccal organs are carried on a distinct 
rostrum ; the appendages of the first pair are either styliform or 
chelate, and the terminal segment of the palp is conical or styli- 
form. The skin is strengthened by a number of dorsal and ventral 
plates. 
These mites are chiefly marine in habit, but a few species occur 
in fresh water. They do not swim, but crawl on algae and marine 
animals. They were first made known by Mr. Gosse, who 
described several British species in the year 1855. 
