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Seeing Moths in a New Light

Submitted by: David G Larson, Augustana Campus, University of Alberta, Canada
Photo credits: DG Larson

More than 6,000 species of moths are thought to be found in Costa Rica, and many hundreds of those moth species are found in the wet tropical forests of Osa Conservation. Micro insects, especially micro moths with wing lengths of less than 1cm, fill the air just after sundown and are often the target of the early evening insectivorous bats. Macro moths with 1-15 cm wing lengths usually become more active later in the evening. The variety in form, color and markings of moth forewings and often the hindwings are as spectacular as their near relatives, the butterflies. Thus moths reward the nocturnal exploration of their biodiversity with surprises that never seem to end.

A few examples of this diversity in mid-February from the trails around Piro Station illustrate this.

Monitoring what light responsive moths are present in particular habitats using ultraviolet illuminated sheets and digital cameras is quite feasible today. Moth photos with significant resolution that can be shared electronically combined with the ready availability of moth photos, identification helps and information on web sites are the key starting points. Because of the unique shape, color and markings of many of the moth species, identifying moths to family, genus or even species levels for particular indicator species is realistic. On top of that, the plant food requirements of moth caterpillers and adults are frequently limited to a particular family of plants or even a particular species, making them a very effective group to use to monitor the health, diversity and integrity of plant communities.

With this in mind, the tropical field studies carried out at Osa Conservation Piro Station in mid-February in 2012-15 by faculty and undergraduate students from the University of Alberta Augustana Campus, Canada, included the compilation of the photos of the macro moths coming to UV light sheet surveys. Sampling a different location each night in primary, secondary and riverine topical wet forest sites on the trails around the Piro Station for six to ten nights each of the four years resulted in 577 photos of at least 239 species of macro moths.

Over 80% of the species photos were singletons, having a single photo of the species over the four mid-February sampling periods, and in the 2015 sampling 50 of the 52 new species were also singletons. In addition, no more than five species were repeatedly encountered in any the four sampling periods. While the high percentage of singleton species in the four February surveys is likely a function of the use of a weak 15 watt UV light source in order to ensure a habitat specific draw distance, the species accumulation curve for moth species around the Osa Conservation Piro Station in the mid-February period has not approached a leveling out yet. Based on this data I project at least 300 species of light responsive macro moth species occur in the forest habitats around the Station in mid-February.

The goal of this study was to make this baseline information about the macro moths present in the forest around Piro Station in mid-Feburary readily available to the Osa Consevation scientific and educational programs as well as to contribute to what is known about the moth biodiversity of Costa Rica. To those ends the Piro Station moth photos were submitted and accepted for posting as an album in the moth section of the University of Georgia Discover Life web site (discoverlife.org) which is compiling a directory to the moths of Costa Rica. The Piro Station moth album is found at: http://bit.ly/1aWPSSQ.

Two moths encountered in the 2015 Piro Station moth survey illustrate some additional things about biodiversity projects such as this.

First, to date this particular moth in the Erebidae family has not been encountered yet at any of the moth web sites nor was it recognized so far by anyone viewing it in the Facebook- Mothing and Moth Watching group. At present three-quarters of the Piro moths still have this nameless or genus name only status. Posting their photos in the Discover Life album and subsequent referrals to moth family specialists may result in some more of them getting named . However, the fact that their photos are in a moths of Costa Rica database at least provides a benchmark for what is present around Piro Station in mid-February that is available to anyone doing any follow-up moth sampling in this area.

Second, the above moth is the white witch moth, Thysania agrippina (Crawer 1776) [24.0 cm wingtip-to-wingtip], also in the Erebidae family, which came in February 2015 to our survey sheet at the junction of the Ajo and Interpretive Trails in the mature primary forest north and upslope of Piro Station. Web information about this moth claims that using the wingtip-to-wingtip parameter, a 30 cm specimen of this species from Brazil is considered to be the largest moth in the world and that T. agrippina is thought to be a relatively obscure species in the Brazil to south-Texas range from which it has been reported.

These two erebid moths reinforce key things about biodiversity sampling for me. The first is that moths are a largely hidden component of biodiversity for most people but once seen, can readily capture people’s imagination. Second, you can never predict what will be found in the next sample you take because new moths are always present. Third, do not stop sampling too soon – four seasons and 39 sheet samples later produced the white witch moth and pushed the bar for my moth bucket list to unforeseen horizons!

For these two moths and for all of the rest of the moths in the Discover Life photo album, I am very grateful to Osa Conservation and all the staff at Piro Station for the opportunity to explore the moth biodiversity on the Station’s pacific slopes of the Osa Peninsula over the past four years and to be able to bring our undergraduate students so they also could experience what this site is about!