Well, we emailed the CO extension agency last year about this exact question, as I had 14 BSTs and only 3 of them were females. They were saying that it was determined when the eggs were fertilized. Since then, as I have researched and learned more, I can support this with what I've learned. It is determined as soon as the sperm combines with the egg cell by the chromosomes. I was just thinking one thing, but looking on the most helpful website I found, I found that the situation in butterflies is reversed from humans. Given that they already have it written out, I'll let them explain it. This site says: Sex is determined, in both humans and Lepidoptera, by sex chromosomes called the X & Y chromosomes. In humans, an individual that is male will have X & Y chromosomes, whereas a female will have two X chromosomes. In Lepidoptera, the situation is reversed -- XX is male and XY (or simply one X and no Y) is female. I should point out that it is the number of X's that is important. In Lepidoptera, an individual with just one X (and no Y) is going to be female. Any individual with two (or more) X's will be male. When cells divide, one complete copy of all the genetic information (DNA) is passed to both cells, or, in other words, before the division there are two complete copies of DNA in each of the chromosomes, which are attached to each other before division. These two copies of the DNA in each chromosome are then separated during cell division. Occasionally, the two copies of a particular chromosome do not detach from each other during cell division (called non-disjunction), and the end result is that one of the cells will end up missing an entire chromosome, which is typically lethal to the cell. The other cell (that gets the unseparated chromosome) may be unaffected, or normal, though problems can occur in this cell as well. However, if a non-disjunction occurs in an X chromosome in an individual that is XX (male in butterflies/moths), that would mean that one of the cells in this division would end up with one X chromosome, while the other would end up with two (or three) X's. In other words, one of the resulting cells (and all cells that came from that cell) would be female, while the other cell (and its descendents) would be male. So, if you have a non-disjunction in an X chromosome in an XX individual during the first division of the zygote, then you will end up with an individual that appears half male (on one side) and half female (on the other side). This is called a bilateral gynandromorph. The non-disjunction can occur during later divisions, however, giving you a smaller portion of the body/wings that looks like one sex and a larger portion that looks like another. It can even happen more than once during development, so that you end up with patches of female and male scattered around on the individual, resulting in what is called a mosaic (see second Tiger Swallowtail, below). VERY bizarre! Before I saw this site, I wasn't aware that there was such a thing as a mosaic individual. It sure is nice having the web at times... While thinking about this, I also realized another interesting fact. I realized that when a BF egg is first laid, it is 1 cell! After all, when a male and a female gamete combine, you end up with 1 cell that then divides into others. Since BF eggs are fertilized virtually as they are laid, that means that the BF egg you see at first is a single, extremely large cell! I mean, that is one giant cell (compared to most, at least)! -Jmcat

I always figured the best time for any moth or butterfly to emerge in spring was when their host plant has started to make new growth, Tiffy. Big moths are only supposed to live about a week, so if they emerge too early, even if they manage to find a partner and mate, what would the female lay her eggs on? She could lay them on bare branches and maybe the eggs could last long enough in cold weather, but wouldn't it make more sense for her to be able to lay her eggs on new growth, which is what they like? So, I put my cages on the front porch when new growth has begun - if I were you, whenever that happens where you are, that'd be the right time. Dan, I saw my first female spicebush swallowtail yesterday, and I think I saw a black female tiger today - I know it was a big black swallowtail, so maybe things are starting to look up. The cecropia and the luna males both left - maybe I'll get a female moth soon. Sherry

I guess their song does have an underwater sound to it, Ken. The wood thrushes nest here every year. This year it appears they're nesting closer to the house than they ever have - I keep seeing them going to and from an area to the east of the garage (detached) and whenever the dogs go into that area, they fuss. I'd love to get a picture of them, and/or see the nest, but one year I tried making a picture of their newly constructed nest, and they abandoned it! :( So, I won't get too close to them - they really seem to love their privacy! Sherry

I'm sure your moths are no longer coupled but for future reference, cecropias will disengage when it gets dark. If for some reason, I need them apart sooner than when the sun goes down, I'll put them in a dark room, set a timer for 15 minutes and then go back in to figure out where the male has flown (since he was on the outside of the cage) so I can let him go. Males can mate multiple times. I put the females in paper bags as soon as I realize they have disengaged. Most tend to start laying eggs soon after disengaging and will continue to lay eggs for a few days. OTOH, I have run into a few that do not like bags. I had one this year that sat for two days before laying eggs. Normally when this happens, I let the girl go and move on to another but this year wild males have been few and far between so I waited her out. Anyway, periodically check on her progress until you have enough eggs and then let her go. If for some reason, you want to lengthen the time you're raising cecropia cats (I do it for teaching purposes), there are two things you can do (that I know about): 1) Experiments show you can keep the eggs in the frig for up to 10 days without affecting the developing cats. Put a few in the frig and you can stagger when the cats are coming out. 2) Raise some on box elder maple (Acer negundo). Some people call it the "poison ivy tree" because young trees resemble poison ivy. Cecropias cats still reach full size but they can take up to 3.5 months to get there. WARNINGS: 1) Heat and high humidity are the enemy when raising cecropias. If they get too much of both, the cats can start dropping like flies, especially if conditions are crowded. If you raise them outside, make sure you have good air circulation. 2) Cecropia cats love to drown themselves so if you are raising them on branches placed in water, do what you can to make it difficult for the cats to reach the water. You mentioned raising them on multiple plants. While the eggs are developing, I suggest taking cuttings from each plant you are considering and making sure each holds up in water for at least 3 or 4 days. Some leaves (including most maples I've tried) wither in nothing flat so they are pretty useless unless you are using rearing bags on the trees. My latest cecropia story: Went to an outside wedding reception yesterday. It was on the west side of town, the area where I release my male moths. So, I took 3 cecropia and 4 polyphemus with me, the plan being my kids would release them somewhere in the area. The kids ended up making a bee line for the pool (this was a very laid back reception) so I took the two containers over to the side of the yard for later. The moths, especially the cecropias, ended up being the hit of the party. I gave many moth talks, lots of people took moth pics and the bride absolutely loved that I brought the moths. Some drunk women apparently did not believe that I planned on releasing the moths and took it upon herself to set them free, greatly disappointing the bride's sister who had not seen them yet. KC