This proposition is well illustrated by the Gasteracanthidae.  Among larvae the warning colors are almost invariably black and white, or black (or some very dark color), in contrast with yellow, orange and red.  These are the colors that also constantly recur among the Gasteracanthidae.

Cases that may be more justly considered exceptions to the rule that these hard, uneatable spiders are conspicuous are such species as Acrosoma rugosa (Fig. 7).  One of this species was sent me by Mrs. Treat last summer.  It lived for several weeks in my window, making no regular web, but hanging among a few irregular strands.  It ate nothing, although provided with insects, but drank greedily of water.  It might seem that its black and white coloring would make it conspicuous, but in connection with its irregular shape and its way of hanging motionless in the web it had the opposite effect.

We have no reason to suppose that the class represented in rugosa is like that touched upon by Poulton, in which very protectively colored larvae suddenly assume a terrifying aspect on the near approach of an enemy; still they do enjoy a kind of double protection.

[Illustration:  FIG. 7.—­ACROSOMA RUGOSA.  Left-hand figure female, right-hand figure male (from Emerton).]

They are inconspicuous, and thus likely to escape attack, but in case they are attacked they have still the advantage of being quickly rejected.  This experience cannot be as fatal to them as to the soft and thin skinned larvae.  Their hard covering and projecting spines would protect them to such an extent as to give them a fair chance of surviving.

In one respect the inconspicuous Gasteracanthidae have a decided advantage over their bright-colored relatives.  The birds, indeed, avoid the conspicuous ones, but their brilliancy serves to attract another enemy against which spines are no protection—­the hunter wasp, which, as we have seen in the work of Bates, sometimes provisions its nest wholly with spiders of this family.  Mr. Smith gives like testimony, saying: 

“Spines on the abdomen of certain spiders would serve as a protection against vertebrate enemies, though they do not protect against the hunter wasps, which frequently provision their nests with these species.”  He adds, however, that most of the spiny spiders are common, and that their colors make them conspicuous; just as butterflies that are protected by an odor are common and bright-colored....

MIMICRY.—­Mimicry, or the imitation of animal forms, while it is a form of indirect protection, differs in no essential respect from the imitation of vegetable and inorganic things.  As Bates has said, the object of mimetic tendencies is disguise, and they will work in any direction that answers this purpose.

In nearly all respects spiders come under the three laws given by Wallace, as governing the development of mimetic resemblances in several large classes.  These laws are as follows: