[Illustration: FIG. 431. Female Zilla atrica, enlarged four times.]
[Illustration: FIG. 432. Middle of web of Zilla atrica with the open
segment and thread to the nest at the left.]
We have three species of Zilla, the females of which are so much alike
that it is almost impossible to tell them apart. The males also resemble
each other closely except in their palpi, which are distinctly different
in the different species. They are of moderate size, the largest about
three-eighths of an inch long, and in general appearance resemble the
genus Steatoda of the Therididæ (p. 119). The abdomen is large and oval
and a little flattened. The legs are slender and of moderate length,
like those of Epeira. The head is rounded in front, and the lateral eyes
are not separated farther from the middle pairs than they are from each
other. The mandibles are large and thickened in the middle toward the
front. The epigynum and the spinnerets are both small. The color of all
the species is gray, with sometimes a little yellow or pink in the
lighter parts. The cephalothorax has usually, but not always, a dark
border at the sides and a middle dark line that widens and becomes
lighter toward the eyes. The abdomen has a wide middle stripe like
Epeira, scalloped at the sides and crossed at the hinder end by two or
three pairs of transverse spots. In front it is almost white or tinted
with pink or yellow, and narrows almost to a point, with a much darker
spot each side. The sides of the abdomen are marked with oblique dark
marks that extend underneath. The sternum has a light middle stripe.
Under the abdomen is a dark middle stripe, with light each side of it.
The legs are pale, with narrow gray rings at the end and middle of each
joint. These three species seem to be the same as three found in
Europe,--_Z. atrica_, _Z. x-notata_, and _Z. montana_. _Atrica_ is found
at Ipswich and Salem on the coast of Massachusetts, _x-notata_ at Woods
Hole on the south coast of Massachusetts, and _montana_ in the White
Mountains and Adirondacks. Wherever found they are in large numbers,
_atrica_ and _x-notata_ living on the outside of houses, and _montana_
in trees and rocks. The webs of Zilla (fig. 432) have a segment left
without cross threads, sometimes for its whole length, and sometimes
only the part of it nearest the center. Opposite this open segment a
thread leads from the center of the web to the nest (fig. 433), which is
a tube of silk open at both ends.
The differences between the palpi of the males are very plain. In
_atrica_ the palpi (fig. 434) are as long as the whole body, with the
femur and tibia both slightly curved and the tarsus and palpal organ
small and like that of _x-notata_. In _x-notata_ (fig. 435) the palpus
is as long as the cephalothorax, and the tarsus and palpal organ small
and round. The front legs are a fourth longer than in _atrica_. In
_montana_ (fig. 435_a_) the palpus is still shorter, the tibia thicker,
and the tarsus and palpal organ larger. There is little difference in
the shape of the epigynum of the different species, but that of
_montana_ is twice as large as that of _x-notata_ or _atrica_.
[Illustration: FIG. 433. Tubular nest of Zilla atrica.]
[Illustration: FIGS. 434, 435, 435_a_. Male palpi of Zilla.--434, Zilla
atrica. 435, Zilla x-notata. 435_a_, Zilla montana.]
$Singa pratensis.$--The Singas are small Epeiridæ a sixth or fifth of an
inch long, with smooth bodies and bright colors. They live among grass
and other small plants in low open ground. When full grown the females
of _S. pratensis_ are a fifth of an inch long, with the abdomen oval and
marked with a double white stripe in the middle and a single one on each
side. The cephalothorax is yellow, with a little black between the
middle eyes not extending to the lateral pairs. The legs are yellow,
without rings or other markings. The abdomen is yellow brown, darker
toward the hinder end, with white or light yellow stripes. The under
side is the same yellow-brown color, darker in the middle, with two
narrow, curved, light lines from the spiracles to the spinnerets. The
males are marked in the same way and have a smaller abdomen and longer
spines on the legs.
[Illustration: FIG. 436. Markings of the back of Singa variabilis.]
$Singa variabilis.$--This is a little smaller than _pratensis_, usually
about a sixth of an inch long. The legs and cephalothorax are bright
orange color. The front of the head between the eyes is black. The
abdomen is usually entirely black, but occasionally has bright yellow
markings (fig. 436) arranged somewhat as in _pratensis_. Sometimes there
is a wide middle stripe, with narrower ones at the sides and two
underneath. Sometimes there are only the two lateral stripes, and there
are all variations between these markings. The males are colored in the
same way and have the same varieties. They are smaller than the males of
_pratensis_, but have the palpal organs as large or larger.