I did not know the answer to this question so I did some research and it turns out that no one knows the answer yet! There are several groups of scientists that study butterflies and moths and they are trying to sequence the genomes but have not finished. The genome is made up of every single piece of DNA a butterfly has.Therefore, once we know the sequence of all the DNA we will know how much there is and since chromosomes are made of DNA we will eventually know how many chromosomes the butterflies have.

Butterflies are insects in the Phylum Arthropoda. Another insect also found in this phylum is the fruit fly. They are small brown flies with red eyes that you may have seen flying around fruit in the kitchen. The important thing about fruit flies is that scientists know a lot about these insects genome. They have been studied for years and every single piece of DNA has been counted. They have over 13,000 genes on 4 chromosomes. So, you might ask, what does this have to do with a butterfly? Since fruit flies and butterflies are both insects they MAY share similar amounts of DNA in their genomes. Although, flies and butterflies are quite different so it is possible they share very little DNA. Only time will tell! You might want to keep track of the butterfly research and I am sure one day you will know exactly how many genes and chromosomes your favorite butterfly has.

You both win! Different butterflies actually have different numbers of chromosomes! The Polyommatus atlantica butterfly of the Lycaenidae family has 446 chromosomes. On the other hand, the Hypothyris thea butterfly of the Nymphalidae family has only 10 chromosomes. Others like the Squinting Bush Brown butterfly (Bicyclus anynana) has 28 chromosomes and the Red Postman butterfly (Heliconius erato) has 21 chromosomes.

Well, I looked online and found both answers. From what I know of genetics, I will bet that it is 20-40, and that it varies from one species of butterfly to the next, just as it varies from one species of mammal to the next. Organisms that have 100+ chromosomes usually acquire them through a process called 'polyploidy', which is a duplication of the numbers of chromosomes. This is almost always fatal in animals (you may know about Down Syndrome in humans, which happens from an extra copy of Chromosome 21 - and that's just ONE extra chromosome, not an entire set), which means that for the most part you only see it in plants and fungi. So I very much doubt that butterflies would have hundreds of chromosomes, but I do not know for sure.

1. I found an article that says butterflies have 30 or 31 chromosomes; but it's an old article from 1978, and scientists have learned a lot of new things since then.

2. Here's a link that says butterflies have about 380 chromosomes and a huge genome, 40 times bigger than ours:

3. Somebody wrote a book called "DNA and Heredity" that says butterflies have 380 chromosomes.

4. I found the best article yet in Nature magazine, which is a very famous science magazine. It says that there's one group of butterflies where the numbers of chromosomes in different species vary from 20 to 268. That article is from 2005, which was not so long ago.

So, I think the number 380 is a mistake, because I can't find that number in any scientific articles. I think there is a big variation in how many chromosomes a butterfly can have, like it says in the Nature article.

So I think you and your teacher are both wrong! Butterflies don't have ~380 chromosomes, and they don't all have 20-40 chromosomes either!

One thing you need to remember about counting chromosomes is that you can count them in 2 different ways to get 2 different numbers - if you count the chromosomes in eggs or sperm, humans have 23 chromosomes. That's called the 'haploid' number. But after the egg and the sperm get together, there are 46 chromosomes, which is 23 pairs.

It was hard to find the answer to your question, and I got the best answers by searching the google scholar site.