When the weather turns cool (below 70 F), cloudy, or rainy, laying slows or stops because monarchs are so affected by temperature. They prefer 84 degrees F.
Your potential for future eggs is good if you have several mated females. When warm weather returns, they'll probably lay. But what to do if you need eggs now? Here's what I tried:
#1: Will a heat lamp, plus a boost of several degrees F indoors, help? I moved the breeding tent into my garage. It's slightly warmer in the garage at night. I pointed a 250 w yellow heat lamp towards the butterflies.
#2: Will full sun outdoors, plus a boost from the heat lamp, help? In the sun outdoors, the temperature was around 60 F, climbing to 63 F. The butterflies all moved to the sunny part but remained mostly inactive. I shined the heat lamp where the butterflies were gathering, about 1 foot away. Some closest to it become more active, but overall, there was little apparent benefit.
Conclusions so far
- A single 250 w bulb doesn't appear powerful enough. (I used one that produces yellow light, not red light). Perhaps several lamps at close range would work better.
- Butterflies are attracted to natural sunlight to "bask." They are less attracted to "bask" in response to one heat lamp.
- Move your outdoor tent into direct sunlight whenever it becomes shaded. A pop-up tent works best because it is easily moved and doesn't require stakes.
We need to consider the benefits of moving indoors versus the disturbance it may cause. If artificial lights don't work or it's not significantly warmer indoors, it may be best to leave the butterflies outdoors.
Conversing with butterflies
"Do you like to warm up with a heat lamp?"
Above, I tried to find out if butterflies would move toward and bask by the lamp. But the butterflies were inactive in the cold, so maybe they were too cold or too "sleepy" to move toward the light. I needed to ask the question using a better method.
#3: A day later, I again tested their reactions to the lamp again. Now they were more active after I finished feeding them.
Three out of 12 butterflies did flutter or bask near the light. But still, not a big vote for the lamp. Is there a way to get a more clear-cut response?
After sundown, I gave butterflies a choice when they left the artificial flower. They could fly to the right where the heat lamp was located, or go left and roost, with a background of dim sky and trees (where they would normally spend the night).
At about 60 F, they had to shiver in preparation and still had difficulty flying. Seven went left, and two right, with one undecided. The ones that went right clearly were basking--fluttering, spreading their wings, or resting in front of the light.
While this suggests that some butterflies choose basking by a heat lamp, an alternate explanation is that at dusk, basking is not a normal behavior at dusk. It's a time when butterflies seek appropriate places--trees--to spend the night. This experiment needs to be repeated during the day when basking is expected. But that would be a waste of time, since I was beginning to suspect the heat lamp is ineffective and a better solution is to control ambient temperature with a thermostat, setting it as high as necessary.
#4: Next, I moved the butterflies indoors. With a room temperature of 75 F plus the heat lamp raising it to 77 F inside the tent, I got 5 eggs the next day. Still, this was sub-normal laying. Some butterflies flying very fast, colliding with myself or the walls, suggested the monarchs couldn't see well in the floodlamp's glare. The females seemed to have difficulty finding the milkweed stem.
#5: To get the females closer to the milkweed, I placed them in two small tents on a tabletop near a window with direct sunlight. The butterflies were confined to within a foot of the milkweed, with the temperature at 75 F. They began to lay at more normal levels: one laid 54, the other 18 that day.
Conclusions--what boosts laying indoors...
- An ambient temperature of at least 75 F (rendering a heat lamp superfluous)
- Confining females close to a milkweed stem helps them find it.
- Natural light is calming and helps them find milkweed. Natural light from windows helps them maintain their photoperiod.
The nuts and bolts of science
I started out asking if the lamp would help warm up the monarchs. I had to continue refining the experiments, ruling out alternative explanations or "noise," until just one conclusion remained.
Factors like time of day or activity level can prevent or hide the response you are looking for--a movement to the lamp. In the "conversation with butterflies," you can't hear the answer if there's too much "noise."
You need to improve not only how you perform the experiment, but also which question you ask. Eventually, I discovered that finding out if monarchs like to bask in the lamp wasn't the right question. A better questions is: "How you can raise their body temperature most efficiently and naturally?" And: "What else can you do to help them lay besides temperature?"