Two of the tiniest families of moths are the Nepticulidae (Pygmy or Minute Moths) and Opostegidae (White Eye-cap Moths). When we say tiny … we mean TINY. When resting, these moths are typically just 2-4 mm long and while the adult moths are active in the late spring and summer, most people in the world will never see them.
These families are sisters, and just like siblings in the human world, they share some features that they have inherited from their last common ancestor. Beyond being tiny, one of their most obvious features is that the base of their antennae is expanded and covers their eyes when they are at rest. While it’s hard to be definitive about the exact evolutionary benefit of specific structures, one possibility is that these eye-caps help camouflage the moth. Eyes are black and contrast greatly with the rest of the moth – which tend to be light brown or speckled in the case of Nepticulidae or bright white in the case of Opostegidae. Having an eye-cover the same colour as your head and body may enable you to blend in better, as a speck of bird poop or a blemish on a leaf.
While adult moths are seldom seen, at least for Nepticulidae, you may see evidence of their caterpillars which eat leaves from the inside and leave characteristic trails or mines as they chew. These caterpillars are so small that they live in and eat only one side of the leaf, so that while their mine is visible when looking at one side of the leaf, it is not apparent from the other. Nepticulidae mine leaves of many types of plants, but in Australia many species mine Myrtaceae leaves (e.g. Melaleuca, Eucalyptus, Lophostemon etc.).
Left: leaf trails of the Nepticulidae
Only 22 species of Australian Nepticulidae have been given names – there are likely hundreds, if not thousands, of new species to discover … so keep your eyes out for mines and maybe even moths, like the one above. Take photos where you can and upload them to iNaturalist and add to our understanding of the fauna of the Bend of Islands.
Compared with Nepticulidae, Opostegidae are even more elusive. Most moths are collected at a light suspended in front of white sheet. While tiny, Nepticulidae stand out as brown spots on the white sheet – whereas Opostegidae are more like a painting by Kazimir Malevich – white on white.
In addition, while Nepticulidae caterpillars make obvious tracks in the leaves in which they feed, Opostegidae caterpillars are more secretive. In Australia, as far as we know, no Opostegidae caterpillar or its tracks has ever been photographed or observed; consequently, we know nothing of the plants on which they depend for food. If Australian Opostegidae caterpillars are like their relatives elsewhere, they may feed inside the stems of plants – which, in addition to their tiny size, is why they are so elusive.
While most Opostegidae adults around the world are tiny and white – one Australian group is positively gigantic having a wingspan of around 8-10 mm and prominent brown stripes on their wings which have a white, cream or yellow background. There is nothing known about this group, which is almost certainly a new genus that currently has no name. These moths have been collected along the east coast of Australia including nearby in Warrandyte in late spring and early summer. If you see a moth like this, please photograph it and let us know. Even better – if you find one associated with a plant – please record the details as this may be the first clue as to where caterpillars feed!
Doug Hilton & Frank Pierce
November 2024
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