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Eggs!

"Where are the pics of eggs?!" was the question sent by e-mail, and yes, other than the eggshell remnant shown at the bottom of this page, the lack of egg pics seems to have been an oversight for a very long time on this website. So it's getting fixed with this page.

Most of the images below, except where noted, were shot with a Microsoft Lifecam HD-5000 webcam running in manual-focus mode.

Eggs tend to be laid, if possible, only on young and healthy growing fronds (fennel leaves). They tend not to be laid on fronds that are old and yellowed at the tips, or that are festooned with general garden crud, spider webs, or aphids. Female butterflies are, to their credit, generally fastidious and desire the best for their offspring: a clean, nourishing, and fresh frond to nibble on after the remnant eggshell is consumed by the newborn caterpillar.

However, it must be admitted that as summer wears on and as the fennel plants go to seed and the seed heads get grungier and more aphid-infested and inhabited by various other insects, the butterfly moms do lay their eggs on these heads because there are no nice fresh frondy places remaining on the plant. Tiny caterpillars can sometimes be found clinging, amidst the grunge, to the flower stems or to the flowers themselves.

Occasionally, eggs can be found on developing flowers or their stems, but they can be harder to find on these more complex structures. 

Below are a few eggs attached where they were recently laid by mom. A dab of sticky glue of some sort is what glues them to the fennel stalk. They adhere pretty firmly and do not fall off.



The eggs are about 1mm in diameter and appear to be perfectly spherical except for a somewhat flattened base where they are attached to the frond.

The image below, taken with a camera built into a dissecting microscope, shows the flattened base and what appears to be a very nice and thorough glue-job to attach the egg to the stem:


The shell of the egg is composed of layers of proteins with a waxy outer layer that reduces water loss. There are tiny pores in the surface to allow air to enter, and a pore large enough to allow the sperm cell to enter to fertilize the egg.

For the first couple of days the eggs are a pearlescent yellowish white and glisten in direct sunlight. They are not in sunlight here.



Then, as the caterpillar embryo develops, the egg will display an orange-brown band around the egg above the equator. The band can be faintly seen on the right side in the close-up two pics above. Then, for a couple of days before hatching, the color darkens and ultimately becomes a tiny curled-up black caterpillar sloshing in liquid if you can examine the egg at sufficient magnification.



An EMPTY egg? It happens from time to time. At least they appear empty. Perhaps they have clear fluid inside. This image was shot through the eyepiece of a dissecting microscope.



Another normal egg below....



Uh-oh -- 1 day later and the brownish band (baby caterpillar-to-be) is clearly visible --- this is embryonic action and makes me suspect that the eggs were not laid as recently as I had thought.



It looks like the caterpillars are well on their way. Whether this fairly sudden change reflects rapid development, an increase in transparency of the shell or contents, or the activation of genes for pigment production, I do not know.



Note the "polar" structure. It is seen in all the swallowtail eggs I have looked at.



The image below was shot with a Canon Powershot SX260 HS camera. The fennel branch is sitting on a paper towel.



Here's a close-up view of an egg looking a bit like a moon of Jupiter. The image was taken with the Canon camera thru the eyepiece of a dissecting microscope. On my screen the 1mm-egg measures about 80mm in diameter, so the magnification on the screen is about 80x. The orange-brown band (caterpillar-to-be) is clearly visible as is the "polar" structure. The black and white specks that you see are on the surface and are of environmental origin--crud of some sort:

Egg features

When looking thru the stereo dissecting scope, the above orange-brown structures appear to be very near the surface of the egg and mostly 2-dimensional. They do not yet appear to be a developing caterpillar floating within. But they are, and that fact becomes much more obvious within a day or so.

Here's another egg at about the same stage of development:

Egg features

Getting very dark--2 days later, the eggs looked like this:





The dark color results from the embryonic caterpillar filling up the egg. At this stage, the caterpillar can emerge soon. The ones above started chewing their way out of the eggs a few hours after the pictures were taken. The actual emergence of the caterpillar happens very quickly and unfortunately none of these was caught in the actual act.

Below is a video shot through a dissecting microscope showing movement of an embronic caterpillar within the egg. Use the full screen to see the movement more clearly. 



Below is another video of the same egg still closer to the time of hatching. At this point, a bubble has formed within the egg at its upper right. Also note the cameo appearance of a very small insect meandering in from the left side about 17 seconds into the video. Use the full screen to see the movement more clearly.



See this same cute little guy chew his/her way out of the egg...