WHEN NATURE DOESN'T FOLLOW THE CALENDAR: an Unexpected Lesson from OIF's Giant Silk Moths

Sadly, this has not been a great year for OIF's giant silk moths.

At least, that's what I thought at first.

As it turns out, nature may have had other plans.

The Polyphemus Moths:

Our Polyphemus moths were overwintered indoors at our facility. They were taken out in May and emerged looking healthy, eclosing around late May and early June as they typically do.

All were placed into individual "calling cages," in which virgin females release pheromones capable of attracting wild males from over 10 km away.

Fig. 1. Virgin female inside a calling cage.

The spacing between the bars is wide enough to allow wild males to mate with the captive females without issue [Fig. 2]. After mating, the male typically flies off before dawn. The female is then transferred to a mesh enclosure or paper bag where she lays her now-fertile eggs.

Fig. 2. Captive-bred female mating with a wild male.

Two females were visually confirmed to have mated, while the remaining two showed strong signs that they had as well. All four laid hundreds of ova, which were maintained under identical conditions using the same rearing methods.

Despite this, only a portion of one brood successfully hatched.

The silver lining was that the successful female happened to be a particularly beautiful orange morph [Fig. 3], the only individual to display that rich orange hue rather than the more typical mustard-yellow coloration [Fig. 4].

Fig. 3. Orange morph Polyphemus moth.

Fig. 4. Typical yellow coloration of the Polyphemus moth.

Hopefully that beautiful colour is inherited by some of her offspring 🤞

The resulting caterpillars, now just over a dozen strong, are feeding well on cut white oak in a mesh enclosure [Fig. 5].

Fig. 5. Polyphemus caterpillar resting.

The Promethea Moths:

A single female Promethea moth also emerged. She successfully called in three different wild males, although she ultimately mated only with the last. While she produced dozens of eggs, only a fraction proved fertile.

Once the larvae hatched, they were divided between lilac and white ash as host plants.

The ash proved disastrous.

Every caterpillar feeding on white ash died within 36 hours.

The lilac-fed larvae performed better, although survival was still poor, and as of this writing only a single caterpillar remains.

Side Note: To rear this species properly, one should ideally use its two natural favourite hosts: spicebush (particularly this species) and sassafras. Lilac is a well-documented substitute in captivity, so my lone remaining Promethea caterpillar still has a fighting chance... it simply would have had a much better one on its preferred hosts.

Lesson learned.

Host plant selection is far more complicated than it first appears. Nutritional quality, defensive chemistry, local adaptation, and even individual preference can all influence success. It's a fascinating subject deserving of its own article, so that discussion for another day.

The Luna and Cecropia Moths

The remaining species at OIF are the Luna and Cecropia moths.

Both have long been favourites of mine, and of countless other nature lovers.

Some animals possess an undeniable presence. A great bear emerging from the forest. An old bull moose standing motionless in a marsh. A freshly emerged Cecropia moth resting quietly on a fence post.

Each seems to radiate an almost tangible aura of significance.

Their beauty is only part of the experience.

What truly captivates is the feeling that you are witnessing something extraordinary.

Their immense wingspans, paired with impossibly delicate colours, give Saturniid moths a presence that photographs rarely capture.

Seeing one alive in person is an entirely different experience.

In any case, these cocoons spent the winter outdoors in mesh enclosures, as I prefer to typically overwinter them.

A portion of each group was brought indoors during early spring but was accidentally kept too warm. Those steady, elevated temperatures triggered emergence roughly 45 days ahead of schedule.

Sadly, timing is everything.

No wild mates were yet flying, and the host trees had barely begun to leaf out.

Without mates, many Luna and Cecropia died out with no offspring.

...but not all of them.

A handful of cocoons had remained outdoors.

Hope still remained.

These precious survivors were placed into a shaded, well-ventilated enclosure protected from both harsh sun and incessant rain.

Then I waited.

June faded into July.

Still...

nothing.

I inspected the cocoons;

No emergence holes from parasitoids.

No parasitoid flies or wasps inside the enclosure.

Since these moths were captive bred, parasitism seemed unlikely, but it is always worth checking.

I picked up a cocoon and gave it the gentlest shake.

Thump...

Thump...

Something shifted inside.

When an insect dies, its tissues gradually dry out. That's why pinned insects can last for decades. The exoskeleton remains, but the internal tissues lose moisture.

Dead pupae become noticeably lighter, often feeling almost papery.

These did not.

They felt substantial.

Alive, perhaps...

Or at least not dead.

Still, there is only one way to know for certain.

You open a cocoon.

This was not a decision I took lightly.

The cocoon itself is not the pupa. It is a remarkable protective structure that shields the developing moth from abrasion, predators, pathogens, fluctuating temperatures, and excessive moisture while metamorphosis unfolds within.

Emerging from that cocoon is also an important part of development. The physical struggle helps force haemolymph, the insect equivalent of blood, into the crumpled wings, allowing them to fully expand and harden.

Opening a cocoon removes one of the advantages evolution has spent millions of years perfecting.

It doesn't guarantee failure.

But it certainly doesn't help.

I selected one Luna cocoon.

The pupae inside was dark, firm, and healthy in appearance.

Its spiracles, the breathing openings along the sides of the body, were clean and free of mould.

I gently pressed on the thorax.

Sometimes a living pupa responds by twitching its abdomen.

Nothing.

That wasn't necessarily bad news.

It could simply have meant they remained in deep diapause.

I had heard stories of delayed emergence and prolonged diapause before, but I had largely dismissed them as little more than anecdote and hearsay.

After more than a decade of breeding Saturniid moths, I had never witnessed it personally.

One of the hazards of experience is that familiarity can quietly become certainty.

Once we convince ourselves something is merely folklore, we often stop asking whether it might actually be true.

Had I investigated sooner, I would have discovered numerous reports from experienced breeders and museum collections documenting moths emerging after a second winter, and occasionally even later.

The formal scientific literature is considerably sparser than that available for agricultural pest species, largely because giant silk moths have received far less research attention.

Even so, a cursory review of the available literature shows that prolonged diapause is a documented life-history strategy in several species of giant silk moths.

Rather than responding simply to the passage of time, these insects appear to integrate winter chilling, spring warming, day length, and accumulated heat.

When environmental conditions are less than ideal, some individuals simply wait.

Another spring.

Another opportunity.

The Luna pupa I opened four weeks ago remains firm.

It is still heavy.

There are no signs of decay.

So perhaps this isn't a story of failure after all.

Perhaps it's simply a story that hasn't reached its ending.

Where Things Stand

As of this writing (August 2026), no Luna or Cecropia moths have emerged from the cocoons that remained outdoors throughout diapause.

Based on:

1. Cocoons from these same groups successfully emerging after being kept at artificially elevated temperatures.

2. The healthy appearance and weight of both the unopened cocoons and the examined pupae.

3. The unusually cool and rainy conditions experienced this year.

...it appears increasingly likely that many, if not all, of our remaining Luna and Cecropia pupae are simply undergoing prolonged diapause rather than having perished.

Although this possibility is scientifically fascinating, it unfortunately means that OIF will not have Luna or Cecropia moths available from our own breeding stock during the 2026 season.

If these moths emerge next spring, however, what initially appeared to be a disappointing year may instead become one of the most interesting observations we've made in more than a decade of breeding giant silk moths.

In the meantime, the Ontario Invert Farm will be seeking reputable breeders capable of supplying wholesale quantities of Saturniid cocoons.

If you're interested in becoming a supplier for the Ontario Invert Farm, we'd love to hear from you.