184 THE ESSEX NATURALIST
the usual smell responses from certain arachnids, including
harvest-spiders, sealed these organs with vaseline and obtained a
greatly delayed response. Unfortunately other workers have not
been able to confirm this and the function of the lyriform organs
remains problematical.
The eyes are simple, that is they are not composed of a number
of facets like those of many insects. They probably serve mainly
for distinguishing light from darkness, or at the most the image,
if such is formed, is probably indefinite and allows only of the
perception of movement.
Harvest-spiders are susceptible to changes of temperature and
humidity. The sense organs serving these functions are not
known.
Dr. Todd (unpublished) has worked out the temperature
preferences for some species. It is notable that those species
with the highest t.p. appear to be mainly southern or to live in
drier or warmer habitats than others.
A humid atmosphere is essential to all harvest-spiders. They
drink water.
The armature is a notable feature of many harvest-spiders,
as for example the various spines and "teeth" which are out-
growths of the exoskeleton, and which attain absurd proportions
in many exotic forms. The fine spines on the ocularium of
Megabunus diadema (Fab.) (Pl. 14 (a)) and the "hood" covering
the chelicerae and palps of Trogulus tricarinatus L. (Pl. 13 (c)) are
examples. The extent to which these structures are protective
is not known. But the odoriferous glands which secrete an
apparently obnoxious substance seem to be a real deterrent to
most invertebrates. These glands have not been observed to
function in immature harvest-spiders amongst which the mortality
rate is undoubtedly high.
Enemies : adult harvest-spiders seem to have few enemies and
most of their difficulties in life are probably of a physical nature
such as changes of temperature and humidity.
Dr. Bristowe (ibid.) records the following enemies: fish
(when harvest-spiders have been caught by the sudden flooding
of streams), frogs, toads, lizards, birds and shrews. The same
author states that predaceous flies, beetles and dragonflies are
not often to be found eating harvest-spiders. Cases of canna-
balism are also recorded; I am able to add to these.
My own records (Sankey, 1949a) include centipedes, insects
(Hemiptera and Coleoptera), spiders, lizard, bird and various
mammals, the latter being tame badgers, a fox and a hedgehog,
all of which ate various harvest-spiders offered to them.
Dr. Todd (unpublished) records nematodes from Platybunus
triangularis (Herbst.) and gregarine worms from other species.