20 August 2013

Curious caterpillars at Sekudu: amphibious?

The Perepat (Sonneratia alba) trees on Pulau Sekudu are now totally denuded of leaves, except for the very low branches.
A closer look and I'm wondering if the caterpillars on the trees can tolerate being submerged?


These were lots of scary hairy caterpillars munching on the green leaves.
I notice that the leafy branches are all below the mid-water mark (as indicated by the dark colour on the nearby rock). This means that these branches would probably be submerged at high tide, especially at high spring tide. Indeed, a few of the caterpillars have their hairs clumped together as if they got wet. Can these caterpillars tolerate submergence at high tide?
I also noticed little red ants crawling over the caterpillars without harming the caterpillars or being harmed by the caterpillars. Do the ants and the caterpillars have a relationship? I still can't figure out the identity of these caterpillars. Please leave a comment if you can help shed light on these curious caterpillars. Thank you!
The Mangrove cannon-ball tree (Xylocarpus grantum) that grows in the middle of the island was bare of leaves on our trip last month. Today, I saw new leaves growing on the upper branches and lower branches. I still saw lots of cocoons on the tree.
On this trip, I checked out the western side of Pulau Sekudu. As seen from the GIS map done and shared by Dr Raju, most of this part of the island is 'higher' and thus more often exposed at low tide. Thus, as expected, there isn't too many 'exciting' finds here. But it is still very much alive.
There are some rubbly parts here with many Haddon's carpet anemones (Stichodactyla haddoni) and some sponges as well as many crabs and shrimp. But it wasn't as 'exciting' as the eastern edge that I explored last month. There were also many Swimming anemones (Boloceroides mcmurrichi), the rubbly area was carpeted with Posy anemones.
There are some clumps of colourful sponges here, some look like a child's crayon drawings!
I saw this very spiky sponge. I'm not sure what is going on.
Some interesting sightings I saw today include this small Noble volute (Cymbiola nobilis) riding on the back side of a large one. Is it a smaller male waiting to mate with a female? These snails eat other snails, so it makes sense for the male to stay as far away as possible from the business end of a female. I've seen this too with Bailer volutes (Melo melo), also carnivorous snails that eat other snails.
I saw many flowery sea pens (Family Veretillidae) here. I didn't notice the tiny shrimps among the flowery tentacles of the Flowery sea pen until I processed the photo. They blend in perfectly with the sea pen and only their little beady eyes give them away.
I also saw many Spiky sea pens (Pteroides sp.). Like other sea pens, it is a colonial animal made up of tiny polyps each with eight branched tentacles. The polyps are held on 'leaves' on another kind of polyp that forms the central 'stalk'.
I saw lots and lots of Stone crabs (Myomenippe hardwickii). Many of them were mums carrying orange eggs in a flap under their bellies, like this mum with only one pincer. There were also many Swimming crabs (Family Portunidae) of different kinds.
The most common hermit crab I saw today were these cute little ones with banded legs.
Among the interesting fishes I saw were several small Kite butterflyfishes (Parachaetodon ocellaris), several filefishes (Family Monacanthidae) and a small Pink-eared emperor (Lethrinus letjan).
I saw one small colony of Spiky flowery soft coral and totally missed the False cowrie that lives on (and eats) the soft coral, until I processed the photo. I only saw one Crown sea star (Asterina coronata) and a few Biscuit stars (Goniodiscaster scaber), but there are still lots of White sea urchins (Salmacis sp.). As Marcus observed, there are now a lot more Plain sand stars (Astropecten sp.) because much of Sekudu has become bare sandy areas. In fact, Kok Sheng found a cluster of many Common sea stars (Archaster typicus).
Hurray! Kok Sheng spotted the patch of Serrated ribbon seagrass (Cymodocea serrulata) that I saw on in 2011. The patch looks to be about 5m x 5m, it's hard to tell in the dark. I also noticed some furrows that looks like dugong feeding trails.
Kok Sheng found this strange nudibranch that I've not seen before. I'm sure Chay Hoon will know instantly what it is.

Pulau Sekudu is off limits since 2007 and requires special permission from NParks. Thanks to NParks for permission and support to do these predawn low spring tide surveys of Pulau Sekudu. Our last survey was in Jul 2013. Thanks to Alan at NParks for permission to visit and to Chay Hoon for organising the trip! And for the rest of the volunteers for helping to thoroughly survey this small but very rich island. More about why I think it's important to regularly survey Pulau Sekudu and Chek Jawa.

Posts by others on this trip

3 comments:

  1. From post: "a few of the caterpillars have their hairs clumped together as if they got wet. Can these caterpillars tolerate submergence at high tide?"

    The matted lateral tufts on the caterpillars could be due to sea spray, or the result of crawling on wet branches. However, inundation-adapted insects & their larvae are able to survive periodic tidal immersion with the help of certain strategies.

    Bigger caterpillars feeding at the mid-canopy level enclose themselves within galleries constructed from live plant parts, dead leaves/ leaf fragments &/or twigs aggregated with silk webbing, frass & their own body hairs. And as pupae, they sequester themselves within watertight silken cocoons.

    For instance, entomologist Robert Lever reported in 1952 that Argyroploce sp. (Tortricidae) moth larvae on young Sonneratia griffithii are able to tie up leaves, which then allow the enclosed larvae to withstand seawater immersion for 4.5 hours.

    In 1955, Lever also reported that Olethreutes leveri (syn. Lasiognatha leveri, Tortricidae) moth larvae, which prefer feeding on the apical/ young shoots of Sonneratia alba & S. griffithii seedlings/ saplings, are observed to roll up the leaves with dense silk to trap air in the interior. These larvae can tolerate tidal submergence for 8.5 hours within their silken webbing. In contrast, experiments showed that unprotected larvae quickly perish when immersed in seawater.

    Borer-type moth larvae like Cenoloba taprobana (Tineodidae) eat into flower buds, flower stalks & fruits, & tightly pack the entrance with frass such that the resulting galleries remain sealed against seawater incursion even when the flowers/ fruits fall to the mangrove floor.

    Other insect larvae & moth species with smaller caterpillars that feed near/ on the mangrove floor respond to rising tides by retreating under the algal mats & rotting vegetation (where there are air pockets), or into sealed burrows at the base of host plants.

    In addition, moth larvae of the Nymphulinae subfamily (Pyralidae family) are generally regarded as aquatic. For example, Eristena mangalis (Common Aquatic Moth) are covered by breathing filaments over their bodies, & also build tube-like shelters in drainage channels under the rotting leaf litter on the mangrove floor.

    Further info:
    * Whitten, Tony (1999) The Ecology of Sumatra. Tuttle Publishing, pp 111.

    * Burrows, D. W. (2003) The role of insect leaf herbivory on the mangroves Avicennia marina and Rhizophora stylosa. PhD thesis, James Cook University -- see pp 22 & 47.

    * Nagelkerken, I, et al. (2008) The habitat function of mangroves for terrestrial and marine fauna: A review. Aquatic Botany, v89, pp 155–185 -- see pp 165.

    * Murphy, D.H. (1990) The natural history of insect herbivory on mangrove trees in and near Singapore. Raffles Bulletin of Zoology, v38(2): pp 119-203 -- see pp 126 & 143.


    And pertaining to the post's title 'Curious caterpillars at Sekudu: amphibious?' ... the case-bearing of Hyposmocoma (Cosmopterigidae) moths endemic to Hawaii can live & feed indefinitely both underwater or on dry land -- & are thus considered truly amphibious.

    * Schmitz, P. & Rubinoff, D. (2011) The Hawaiian amphibious caterpillar guild: new species of Hyposmocoma (Lepidoptera: Cosmopterigidae) confirm distinct aquatic invasions and complex speciation patterns. Zoological Journal of the Linnean Society, v162(1): pp 15–42

    * A Moth That Has Evolved To Breathe Underwater And In Air (io9 Science News - 22 Mar 2012)

    ReplyDelete
  2. From post: "I still can't figure out the identity of these caterpillars."

    These laterally-tufted larvae are characteristic of the Lasiocampidae (lappet moth) family.

    Your photos of the last-instar caterpillars (pic1) & large whitish spindle-shaped cocoons (pic2, pic3) resemble the description for Suana concolor (Walker 1855, Lasiocampidae).

    From 'The Fauna of British India: Moths Vol. I' (G.F. Hampson, 1892):

    [pp 402] Family Lasiocampidae:
    "Larva with lateral downwardly-directed tufts of hair, and often subdorsal tufts or dorsal humps on anterior somites thickly clothed with hair. Cocoon closely woven of silk and hair."
    -- see the drawing of Suana concolor larva on the same page

    [pp 406-407] Suana concolor:
    "Larva pale brown covered with numerous black striae; 2nd and 3rd somites [segments] with raised dorsal humps covered with close black or dark brown hair; some specimens (or a younger stage ?) have small white-haired dorsal papillae on 4th to 10th somites, each with a pair of red-brown papillae in front and a pair of crimson papillae on each side; 11th somite with black dorsal tuft; lateral brown tufts on each somite; head longitudinally banded with black."

    The Sabah Forest Dept also has a description of Suana concolor larvae & cocoon (17cm long) found on Acacia mangium [Sepilok Bulletin 1: 63-65, 2004].

    More info about Suana concolor:
    * Thai Bugs: Photo of live adult male

    * Moths of Borneo: "Pupation is in a large stout, spindle-shaped silken cocoon. Recorded host-plants: Sonneratiaceae (Sonneratia)" etc.

    Entomologist Ronald Senior-White reported in 'A note on Suana concolor' (Spolia zeylanica Vol XI - Colombo Museum, 1903, pp 299-302) that the fully-grown larvae reach 140mm (female) & 75mm (male) long in the wild.

    Curiously, he also pointed out that none of his reared specimens displayed the "dorsal papillae on segments 4 to 10, each with a pair of red-brown papillae in front and a pair of crimson papillae on each side" that Hampson saw in some wild specimens. See Senior-White's drawings of reared S. concolor as shown in the above paper, where Fig.6 = 4th instar (1x scale).

    Also, the 1st & 2nd larval instar of Senior-White's reared specimens are described as having a "body ringed black and white" & "abdominally dorsally there is a broad blue band".

    Meanwhile, the upper-left corner of your larval "group photo" shows a lone younger instar whose body is ringed REDDISH & white, with bluish tints (or image artifact ?) on the ventral side. I'm wondering if the caterpillars as shown in your photos might be a local morph/ variation or an unnamed subspecies. Do you have a higher-res version of this photo, or a close-up image of the said larva ?


    Similar-looking Lasiocampidae larvae include the various Streblote (syn. Taragama) species. For instance, Streblote siva is a leaf-defoliator of Sonneratia apetala.

    For comparison:
    * Streblote panda -- photos of late-instar larva, all stages

    * Streblote siva -- photos of adult, [scroll down for] early instar larvae, pupa case

    ReplyDelete
    Replies
    1. Thank you Pat for all these details! I shall slowly go through all your links to learn from them.

      Delete

LinkWithin

Related Posts with Thumbnails