From Alexander Wallace   25 February 1868

Dear Sir

Though not a convert to your views, I shall be glad to aid you, by an information I can afford. Possibly however, if you more fully explained the exact point you wished to work out, I could keep it in view in my experiments on Silkworms & aid you by more accurate information—¹ So many numerous extraneous accidents interfere with the life of silkworms as to render it very difficult to arrive at accurate conclusions— For instance your 1^st question has reference to the proportion of sexes. Now do you wish for information on this point as regards a whole brood brought up from the entire no of eggs laid by two healthy parents only? Or do you apply to your question to the mixed eggs of a no of silkworms exposed to all the accidents of outdoor life— In the former case I apprehend the information might at first sight be more trustworthy but then a probably disturbing cause would come in to operation viz the effect of domestication, a better supply of food, and mans interference.— In the second case, the accidents to silkworms from enemies weather &c are so numerous that information for large numbers could alone in my opinion be trustworthy.

As far as my observation is worth anything I believe the males slightly exceed the females in number—. I know they come out earlier and are abundant before the ♀s are numerous— subsequently the females are more numerous than the males.

I have now 1000 pupæ of B. Cynthea² sent to me by a friend not of my own rearing: these are out of their cocoon & could perhaps easily be separated, but error might creep in. In my experiment, the cocoons are strung up inside a canary House where the moths emerge and pair as in a state of nature the trees growing inside— It would be easy for me another year perhaps to obtain some more accurate information for you if you wish it—on this point.³

I have seen it stated by French writers on the silkworm that the sexes are evenly distributed: vide also Count Dandolo p. 242: ‘S’il y a plus des males il faut les jeter, s’il y a plus des femelles, on peut leur donner les males, qui aient été deja accouplés: he goes on to say that the offspring of the second union of the same male with a second female—is by many not considered so vigorous, as the offspring of the first union,⁴ and this I believe, vide also an experiment of mine—Ailanthi culture. p. 203–p 207 is detailed the history of a brood of 101. cocoons, out of which 39 ♀s 46 ♂s emerged, and afterwards ♀ 9. & ♂ 6.— It is a common thing for the same male to unite himself to a second perhaps even to a 3^rd female—.⁵

2 I have seen 2 or more males flying about the same ♀   I never saw them fight. the same thing may be noticed in the common white butterfly—

It is no uncommon thing for me to find in the morning ♀ & ♂ united on a leaf or cocoon, & a 2^nd male close by, asleep, with his tail in the direction of the ♀ body, as if he had been just anticipated by the male in possession

3 I do not think the ♀ evince any choice. I have had frequently 300 or more moths at large in my ailanthi, & only there some of the most vigorous ♀ will be found mated with much stunted ♂ and vice versa—though in a less degree—for I apprehend the amount power of attraction in the ♀ depends on her vitality and if she is weakly—the vigorous male will be attracted to a more vigorous neighbour than she—⁶ But a male with his wings rubbed will probably have also his tarsi broken, & then he cannot effect coition, not being able to alight & steady himself: and this almost always occurs to the male when about 3 days old. Coition therefore to be effectual must take place early—at least in the case of the male— Once knocked about he would be unable to perform his duties. But I do not think that the ♀ is alive & sensible to all this. She is very passive & quiet—extruding her ovipositor—and the first that arrives, suceeds.

Lastly: as to B Cynthia: the ♀ emerges before 8 oclock pm. She generally copulates that night, & remains in cop till the following evening, when she at once begins to deposit her eggs. I think you would be interested in my essay on ailanthiculture, where I have closely detailed the life history of Cynthia.

I shall be at all times willing to render you what aid I can

Yrs truly | Alex Wallace—