How to read a butterfly's mind

It's easy to read a dog's mind.  Dogs are wildly expressive!

Butterflies are slower to give up their secrets.

Those of us producing eggs for schools are under pressure to deliver the goods.  We need to predict if the butterflies will lay enough for the orders we have.  

So, we have to read their minds. "Feeling romantic?  In the mood to lay?"  Here's how to find out what's on their mind.

"Motivation" is a key driver of behavior, for both humans and animals.  Motivation is something we infer from observing a human or animal.  Common motivations are hunger, thirst, sex, fear, and migration, to name a few.  When I joke about "reading their minds," I'm really suggesting we find out their motivations by observing what they do.

With monarch butterflies, there's a complication.  By this time of year, some adults have eclosed with their bodies optimized for migration.  They have stronger flight muscles and larger fat (fuel) deposits. Sex organs are immature to save weight.  They cannot reproduce until spring.  We say that are "in reproductive diapause."

Others, which I call "reproductives," are capable of mating and laying eggs 3 to 5 days after emerging.  Even if you saw them eclose, you can't tell who is who by looking at them, because the incrrase in the percentage of migratory adults, starting around mid-August, is gradual.  

We have to look for signs of motivation to reproduce... Signs that they are ready to engage in sexual behavior and egg laying.

1. Mating indicates a high probability that the male or female is a "reproductive." Egg laying could begin within a day or so, to a week later.  This is only a potential.  To actually get eggs, you need to assure that female doesn't escape or get injured, that she remains well-fed, and isn't distracted into more matings.  Finally, she won't lay without good weather (sun and temperatures over 75 F), and access to milkweed stems she approves of.

2. Tasting milkweed with the front legs, by females, is a weak indicator or being a "reproductive."  They may lay within a day, but more often it takes days before laying begins.

3. Aggression by males is a strong indicator of being "a reproductive."  Aggressive males may "pounce" (drop out of the air) on another male or female, or wrestle (grapple) with others.  If you see them extend their abdomen towards the other, that's a strong sign of sexual motivation.  Repeated or persistent aggression is also a strong sign.  Don't confuse aggression with the commonly seen climbing on one another to get into a take-off position, which is not aggressive.

You can use these behaviors to decide which butterflies are migratory, releasing the migratory ones provided you have enough reproductives.  It may take a week after eclosure before a butterfly reveals its reproductive status.

There's more than motivation to consider

You may be feeling "hungry," but you're not going to eat spoiled food.  Motivation is what puts an animal in a state of readiness to "do something," but it still has to find the right "something" --the right partner, the right food, or the right conditions.   Even if you are hungry, you may not decide to eat outdoors during a blizzard.

Learning a butterfly's motivation to reproduce is the first step.  Discovering other things that affect her probability to lay is more difficult. Here's an example.

I am trying to get more eggs from Female #7.  She laid 155 over the two previous days of warm, sunny weather, but only 11 today, despite the fact that the weather was even better.  Why did she lay fewer eggs today?  What can I do to increase her output?

The answer is to consider possible explanations for the reduction in laying, then look for evidence:

1. She is weeks old and could be near the end of her "laying" career.  Unlikely.  She has only laid a few hundred eggs. Monarchs are easily capable or 700 or more.
2. She has poor nutrition.  Unlikely.  Notes show she has fed well every day.  I saw her feeding on her own when I first supplied the milkweed stem.  Today I supplied some fruit to help rule out a diet deficiency.
3. She needs an additional mating, when she receives a food packet from the male, to continue laying. Unknown. Wait to see what happens if she mates again.
4. Injuries prevent her from laying.  While both wingtips are missing, this is not a handicap. She flies well. All legs and claws are working.  Evidence is strongly against this hypothesis.
5. She didn't like the milkweed stems I provided for laying.  The first stem was rather old and crusty; she laid only 9 eggs on it.  When I then provided a fresh, tender stem, only 3 eggs resulted after hours of access in perfect weather.  However, this stem had small leaves that might have been hard to grip and lay on. So, I provided a third stem, "just right" as in the "Three Bears" story.  No eggs were laid.  This is beginning to look like...
6. She ran out of eggs and needs time to create more internally.  If she lays upon return of good weather, that's more evidence for this explanation. But I have seen some females lay well over 100 eggs in one day. 

So far, it looks like hypothesis #6 is the best explanation.  We have to wait to see if she resumes laying, while trying to keep her safe, giving good nutrition, and providing good milkweed to lay on.

Here's still another explanation, although hard to test

    7. She wants to migrate south. You are thinking: "Wait, I thought she was "non-migratory" because she laid eggs."  That's right.  However, I just read that citizen science observations recently revealed that some "reproductive monarchs" do move south at the end of the summer as they continue to lay.

If true, this is an amazing observation showing how complex and adaptive monarch behavior really is.  The longer nights and cooler temperatures of September slow down caterpillar development. Its possible eggs laid at the end of summer wouldn't eclose in time to migrate.  But by moving a few hundred miles south before they finish laying, reproductive females can "turn up the thermostat" to speed development of their young before winter arrives.  This adaptation can squeeze in an additional generation, augmenting monarch numbers, increasing their "fitness."

Today, I did observe some evidence for explanation #7.  Over the last several days, female #7 has been relatively inactive, resting most of the day when she wasn't laying.  But today, she was more restless, flying around the tent.  I code this behavior as "Flighty," or "Fl."

If reproductive monarchs are flying south to lay, what could trigger this change?  One thing might be a big nighttime drop in temperature.  But last night dipped to only 67 F.  Declining day length is another possibility.

It's not easy reading a butterfly's mind

It takes patience, observation, and notes.  You have to acknowledge you don't have the answers and keep your eyes open for clues.  You also have to maintain high standards of care.  Otherwise, the most basic things--like poor nutrition--could cause your breeding program to fail.

Poor nutrition could result from fermentation of honey water if prepared in advance and not refrigerated, because fermentation could reduce the sugar content.  On a hot day, artificial flowers in the sun could ferment rapidly if scrubbies hadn't been sterilized.  Solution: microwave scrubbies for 60 seconds to sterilize them, then dry thoroughly.

Details matter.  I was thinking about the lack of eggs while I was cleaning artificial flowers.  I noticed how hard it was to get the excess water out of the scrubbies.  I thought: "What if someone sterilized them with bleach, but didn't remove the bleach residue by rinsing and careful drying?"  The residue could poison the butterflies.  More likely, they would be repelled by the bleach odor and simply not feed.