[Odonata-l] Disappearance of Damselflies in SE US?

[Hal White]

Dennis,

The statement below is about the disappearance of damselflies that I 
posted to the Ode listserve five years ago on July 8, 2002 in response 
to similar comments you made about the dearth of Odonates at some 
attractive habitats in West Virginia. What I said in 2002, I could say 
today. This was at a pond that never dries up, so drought isn't the 
whole story.

If this is a demise of damselflies, it needs to be documented and 
studied more systematically. I suspect it has relatively less to do with 
climate change and a whole more lot to do with fouling our environment. 
Sounds to me like a parallel to Silent Spring except we don't know the 
cause and fewer people care enough about bugs now than did about song 
birds then. Are there any graduate students out there looking for thesis 
projects?

Hal
---
(July 8, 2002) Where have all the Zygops gone, long time passing…

Almost exactly 23 years ago, I spent a day collecting at Trap Pond State 
Park in southern Delaware. This past weekend, I returned for a couple of 
hours of collecting hoping to find Enallagma pallidens and E. dubium 
(Pale and Burgundy Bluets), southern species that I had last found there 
in 1979 and 1991, respectively.  Not only were those species absent, I 
hardly saw any Zygoptera! I saw 5 individuals of 4 normally common 
species and none were Enallagmas. In 1979, I collected or saw 15 species 
of Zygoptera, including 9 species of Enallagma, some of which were 
common. I did not notice a great difference in the diversity or numbers 
of Anisoptera except that Libellula luctuosa (Widow Skimmer) and 
Celithemis eponina (Halloween Pennant), which were not seen in 1979, are 
fairly common now.

While it is certainly true that I did not spend a whole day like I did 
in 1979, which might explain my missing a few species, I think the 
conclusion that damselflies are much less apparent now than in 1979 is 
inescapable. The cause is difficult to pin down with certainty, but I 
suspect it is linked in some way to agricultural runoff that has led to 
eutrophication of many aquatic habitats in the area, particularly in the 
last decade. The pond now experiences tremendous algal blooms in which 
the algae is physically removed by harvesters. One consequence is that 
the pond closed its swimming beach several years ago. I also notice that 
certain types of aquatic vegetation, e.g. lily pads, which were common, 
are missing. The pond still supports fish and fishermen. At least two 
species of large freshwater bivalves are common. Crayfish are present. 
Whatever the effect is on Zygoptera, it hasn't greatly affected 
Anisoptera and several other groups of aquatic organisms.

Have others noticed this pattern? Does anyone have an idea about why 
Zygoptera, as a group, might be preferentially affected? Do algae 
produce toxins that affect Zygoptera, but not Anisoptera? Are there 
pesticides found in agricultural runoff that have differential suborder 
toxicity?

Hal White


Dennis Paulson wrote:
> Thanks, Hal.
> 
> I suspect drought plays a big part in the abysmally small number of 
> odonates of all kinds we saw during the Southeastern DSA meeting in sw 
> Georgia. One thing I've found on several recent trips is that 
> damselflies are virtually absent from the southeastern coastal plain in 
> June and July. I saw <100 Enallagma of only 4 species in 2 weeks on two 
> different trips to north Florida and south Georgia, in the field 
> constantly. I. posita and ramburii were both rare, in fact I saw more 
> kellicotti. Lestes were virtually nonexistent. I don't think that was 
> the case when I was active in that area in the mid 1960s, and my field 
> notes bear that out. It's quite perplexing and disheartening. After this 
> recent trip, I'm now thinking that odonates are in a lot more trouble 
> than I had realized. Stream damselflies (Calopteryx, Argia) were present 
> in greater numbers, perhaps as many as normal in some areas.
> 
> Dennis
> 
> On Jul 5, 2007, at 5:37 AM, Hal White wrote:
> 
>> Dennis, Several species of Lestes (australis, forcipatus, congener) 
>> that used to be regulars at local vernal ponds have virtually 
>> disappeared on the Delmarva Peninsula since a drought we had 4-5 years 
>> ago. The ponds were essentially dry for about 13 months. Sympetrum 
>> ambiguum, also from those sites, is just coming back. Hal
>>
>> Dennis Paulson wrote:
>>
>>> For those who aren't familiar with this website, it's a reminder of 
>>> where we should expect drought conditions on our Odonata field trips 
>>> in the United States. It seems everywhere I go in the last decade is 
>>> going into or just getting out of drought conditions. It wasn't that 
>>> way several decades ago. We should be talking about "global drying," 
>>> and this is something that surely will have profound effects on 
>>> odonate populations. I've seen that already in the Pacific Northwest. 
>>> We are out of a drought period now, and it will be interesting to see 
>>> if species return that disappeared from large areas of shallow ponds 
>>> that dried up for several years.
>>> http://www.drought.unl.edu/dm/monitor.html
>>> -----
>>> Dennis Paulson
>>> 1724 NE 98 St.
>>> Seattle, WA 98115
>>> 206-528-1382
>>> dennispaulson at comcast.net <mailto:dennispaulson at comcast.net>
>>> ------------------------------------------------------------------------
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