Weird Science

The Common Rough Woodlouse in a Choice Chamber: Animal Experiments

Polish ver­sion is here

The fol­lo­wing article was ori­gi­nally publi­shed in the jour­nal for edu­ca­tors Bio­lo­gia w Szkole (eng. Bio­logy in School) (2/2021):

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Ples M., Pro­sio­nek i komora wyboru. Doświad­cze­nia na zwie­rzętach (eng. The Com­mon Rough Woo­dlo­use in a Cho­ice Cham­ber: Ani­mal Expe­ri­ments), Bio­lo­gia w Szkole (eng. Bio­logy in School), 2 (2021), Forum Media Pol­ska Sp. z o.o., pp. 52-56

Bio­logy, like all natu­ral scien­ces, relies on hand­s‑on expe­ri­men­ta­tion. In school or uni­ver­sity labs, howe­ver, set­ting up obse­rva­tions with live ani­mals often pro­ves chal­len­ging. Main­ta­i­ning cul­tu­res is regu­la­ted by strict gui­de­li­nes and can be a bur­den. One prac­ti­cal wor­ka­ro­und is to use fami­liar hou­se­hold spe­cies. While ham­sters, mice, and rats are clas­sic cho­i­ces for maze­‑ba­sed beha­vior stu­dies, cats or dogs would be imprac­ti­cal.

Any ani­mal expe­ri­ments — or their use in edu­ca­tion — must be appro­ved by the appro­priate ethics com­mit­tee, espe­cially if they may cause pain or stress. Cur­rent legi­sla­tion in Poland covers ver­te­bra­tes and the most com­plex inver­te­bra­tes (i.e., cepha­lo­pods Cepha­lo­poda), but not other inver­te­bra­tes. I urge you to check the latest regu­la­tions. Even where appro­val isn’t nee­ded, we must never tole­rate unne­ces­sary cru­elty to any ani­mal.

In a pre­vious article, I descri­bed a maze expe­ri­ment with ter­re­strial iso­pods (Photo.1) [1] [2].

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Photo.1 – Sub­ject just before ente­ring the maze

Since our woo­dlo­use coo­pe­ra­ted so well, I’ve desi­gned new trials fea­tu­ring the same spe­cies.

About the woo­dlo­use

Woo­dlice of the genus Por­cel­lio are often mista­ken for insects Insecta but are actu­ally ter­re­strial cru­sta­ce­ans Cru­sta­cea in the order Iso­poda. Unlike most cru­sta­ce­ans, they live enti­rely on land, pre­fer­ring damp habi­tats. Both insects and cru­sta­ce­ans belong to the phy­lum Arth­ro­poda. In Poland, about a dozen Por­cel­lio spe­cies occur [3], the most com­mon being the rough woo­dlo­use Por­cel­lio sca­ber Photo.2).

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Photo.2 – Woo­dlo­use on decay­ing bark

Look for them under sto­nes, in wall cre­vi­ces, among leaf lit­ter and rot­ting wood, or even in cel­lars and gre­en­ho­u­ses [4]. You might also enco­un­ter Oni­scus asel­lus and pill­bugs Arma­dil­li­dium, which roll into defen­sive balls. All make excel­lent sub­jects for sim­ple beha­vio­ral tests.

No ani­mal sho­uld ever suf­fer or be kil­led unne­ces­sa­rily. Despite their chi­ti­nous armor, woo­dlice are deli­cate. Han­dle them gen­tly and house them in a dark, wel­l‑ven­ti­la­ted con­ta­i­ner with sli­gh­tly moist soil or peat plus leaf lit­ter or wood sha­vings. Keep the tem­pe­ra­ture aro­und 20–22 °C (68–72 °F). Under these con­di­tions, they remain heal­thy for days, even up to two weeks, with occa­sio­nal plant mate­rial for food.

Woo­dlice pose mini­mal risk: they’re not veno­mous and unli­kely to tran­s­mit serious patho­gens, tho­ugh they inha­bit decay­ing mat­ter that can har­bor micro­bes.

For full ana­to­mi­cal deta­ils, see my pre­vious article. Brie­fly, P. sca­ber rea­ches about 17 mm (0.67 in) in length, with a dor­sal sur­face cove­red in tiny tuberc­les. Males are blu­i­sh‑gray; fema­les and juve­ni­les are ligh­ter and spec­kled. Some spe­ci­mens are brown or orange [5] [6]. Noc­tur­nal by nature, they navi­gate using tac­tile and che­mi­cal cues. Their vision is limi­ted to two small com­po­und eyes of about 20 omma­ti­dia each (Photo.3).

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Photo.3 – Com­po­und eye (arro­wed)

They walk on seven pairs of tho­ra­cic legs, have ven­tral mou­th­parts, and bre­a­the thro­ugh two pairs of ple­o­po­dal lungs. At the rear are the tel­son and uro­pods. Fema­les carry eggs and juve­ni­les on their ple­o­pods for 40–50 days. Life­span can reach two years, so they seek shel­te­red over­win­te­ring sites.

Expe­ri­ment

Buil­ding the cho­ice cham­ber is sim­ple. Use a ~10 cm (4 in) Petri dish, glass or pla­stic. Divide it into two halves: one side with a desic­cant (acti­va­ted mole­cu­lar sie­ves, silica gel, etc.), the other with damp cot­ton or fabric. Cover with a porous over­lay (e.g., a pla­stic lid punc­tu­red with a nee­dle). The setup is shown in Photo.4.

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Photo.4 – Cho­ice cham­ber with per­fo­ra­ted divi­der

Place about 10–20 woo­dlice on the divi­der, cover the dish (Photo.5), and distri­bute them evenly.

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Photo.5 – Star­ting the trial

Then cover half the dish — per­pen­di­cu­lar to the divi­der — with black paper (Photo.6) and illu­mi­nate from above or place in a bri­ght room. Let run 15–45 minu­tes without distur­bance.

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Photo.6 – Trial in pro­gress

The cham­ber divi­des into four zones (Fig.1):

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Fig.1 – Cham­ber lay­out

After­ward, note each woo­dlo­use’s loca­tion. A typi­cal result is shown in Photo.7.

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Photo.7 – Typi­cal out­come

Most woo­dlice con­gre­gate in Zone II (humid-dark); some in Zone III (humid-light). Dry zones are avo­i­ded. Across 50 trials, the ave­ra­ges (Table 1) were:

Zone % of woo­dlice
I (dry & dark) 6 %
II (humid & dark) 72 %
III (humid & light) 21 %
IV (dry & light) 1 %
Tab. 1 – Expe­ri­men­tal results

Your results may vary, but the ove­rall trend sho­uld hold.

When done pro­perly, woo­dlice expe­rience no harm and can be rele­a­sed back into their ori­gi­nal habi­tat.

Expla­na­tion

In this expe­ri­ment, we obse­rved a fasci­na­ting beha­vio­ral phe­no­me­non. Orga­ni­sms have evo­lved diverse move­ment stra­te­gies and mecha­ni­sms. Nastic move­ments — seen in tou­ch‑sen­si­tive plants like Mimosa pudica or Ber­be­ris vul­ga­ris and spe­cia­li­zed growth move­ments, such as the trap lea­ves of Dro­sera capen­sis, are exam­ples [7] [8] [9]. There are also taxes, tro­pi­sms, and other respon­ses [10].

Ano­ther intri­gu­ing form of move­ment is kine­sis [11], a non‑di­rec­tio­nal loco­mo­tor response to sti­mu­lus inten­sity. Kine­sis can be posi­tive (move­ment incre­a­ses with stron­ger sti­mu­lus) or nega­tive (move­ment decre­a­ses when the sti­mu­lus inten­si­fies). It’s gene­rally divi­ded into two types:

In woo­dlice, kli­no­ki­ne­sis appe­ars as alter­na­ting turns, pre­ven­ting cir­cu­lar move­ment and ena­bling a zig­zag path — vital for navi­ga­ting cre­vi­ces and esca­ping pre­da­tors. Today's expe­ri­ment demon­stra­ted ortho­ki­ne­sis: woo­dlice show nega­tive ortho­ki­ne­sis to humi­dity (they move faster in drier air) and posi­tive ortho­ki­ne­sis to light (they move faster under bri­gh­ter illu­mi­na­tion). As a result, even without direc­tio­nal sen­sing, they tend to con­gre­gate in the most favo­ra­ble envi­ron­ment — humid and dark. If they wan­der into drier or bri­gh­ter zones (where they’re more expo­sed to pre­da­tors and risk of desic­ca­tion), they speed up until they return to sui­ta­ble con­di­tions. Woo­dlice also exhi­bit aggre­ga­tion beha­vior, as obse­rved here.

Note that these sim­ple respon­ses, com­bi­ned with other mecha­ni­sms, ena­ble the woo­dlo­use to achieve cri­ti­cal goals: survi­val and suc­cess­ful repro­duc­tion.

Refe­ren­ces:

All pho­to­gra­phs and illu­stra­tions were cre­a­ted by the author.

This text has under­gone sli­ght edi­to­rial modi­fi­ca­tions com­pa­red to the ver­sion publi­shed in the jour­nal to bet­ter suit online pre­sen­ta­tion.

Marek Ples

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