Seasonality and Multiple-brood Species

  When we speak of the seasonality of any species of moth we are generally referring to the flight period of the adult moth. In single annual brood species the adult flight period may be just a few days out of the 365 day year. Most of the life of a moth is spent in the egg, larval and pupal stages. For many moths little is known of these stages and even the flight periods may be imperfectly known. The moth season can be very different in Canada and the northern tier of states in the USA compared with middle-latitude states or those of the far south. A species that is single-brooded in the north may have several broods in the south. Flight periods may precede slightly or occur in synchrony with the leafing out of specific vegetation required for the development of caterpillars. There is no one-size-fits-all pattern for the life style of moths. In tropical Florida some species may be active year-round.

Seasonality data are provided below for just a few species displaying different patterns of flight periods. Accurate data can be compiled only by extensive collecting and record keeping. Vernon A. Brou, Jr., of Louisiana has been doing this daily for 35 years (except for a recent break caused by Hurricane Katrina). To date Vernon has published in Southern Lepidopterist's News more than 100 brief articles with photos and graphics like those shown here.

  Virgin Tiger Moth -- Grammia virgo -- Single-brooded Species
Vernon A. Brou, Jr. -- previously published in Southern Lepidopterist's News

This species, while broadly distributed across eastern North America, is only rarely found in the deep south. In Maryland (John Glaser unpubl. mss.) it is abundant across the State but adults fly only within the restricted period of July 21-Sep. 3. The short flight period, both in Maryland and in Louisiana, indicate that this species has but one annual brood. The later flight period in Louisiana might be an avoidance of the hottest period of summer there. Host plants include members of the Chenopodiaceae (Goosefoots, Amaranths) with June-Oct. growth periods as well as clovers, lettuce and plantains.

  Bog Lithacodia Moth -- Deltote (=Lithacodia) bellura -- Multi-brooded
Nolie Schneider

Jim Vargo Jim Vargo

This is a species that is probably single-brooded in the north of its range (as far as Newfoundland) and multi-brooded in the south. In Maryland (John Glaser, unpubl. mss.) it is found flying in wetlands across the state from May 23-Aug. 20. This would be sufficient time for two broods. Vernon Brou's chart below clearly indicates three broods at the single study site in Louisiana where he has recorded the species. This species is known to be associated with bogs and Vernon notes that he finds it most abundantly where Pitcher Plants are also found. However, the larval moth's host plants are unknown.

In Louisiana Vernon Brou sees a distinct difference in forewing coloration between spring (browner) and summer (yellower) broods. He also comments over the fact that after finding none of these moths in his traps for 10 or more years they began to show up in numbers low at first but increasing in subsequent years. It is unknown if this is due to vegetational succession. Many such mysteries remain to be discovered through long-term collecting.

Graphics Vernon A. Brou, Jr. -- previously published in Southern Lepidopterist's News

  Io Moth -- Automeris io -- Multi-brooded




The Covell Field Guide credits this species as having one brood northward (Manitoba-Quebec-Maine) and two or three broods southward (Texas-Florida). In Maryland (John Glaser, unpubl. mss.) the flight season runs from May 26 to Aug. 25, which would allow for two annual broods, with the late brood overwintering as pupae. Vernon Brou has discovered four annual broods in Louisiana.

As shown in the chart below, with brood peaks indicated, the longer flight season in Louisiana allows for four annual broods with the peaks spaced at about 46-day intervals. In contrast to the previous chart for Deltote bellura based on 176 specimens over the years, the chart in this case is based on 3,604 specimens and clearly indicates the relative size of broods. The last brood of the year is by far the largest. So, why isn't next year's first brood also large? Many of the overwintering cocoons and pupae are destroyed by predators, accidents and the elements.

Photos and Graphics Vernon A. Brou, Jr. -- previously published in Southern Lepidopterist's News

MothTalk/MothTalk018.htm -- 01/15/2007