Inchworm and Longworm Chess
By Ralph Betza
Today we turn to nature for a gentle inspiration about how to be in two places at once when you're not anywhere at all, and then descend into the Dungeons of Doom to expand the idea by cutting it in half.
The Inchworm in NatureConsider the lowly inchworm, so beautiful a shade of translucent green, as it spends its life gently measuring its path.
First it stretches its face to touch a new place, then brings up its rear until both are near.
It does not buzz, it does not sting, the inchworm is gentle and serene.
The Inchworm in Chess
The 64 squares are a violent place, and so the gentleness of the inchworm cannot be emulated in a game of Chess; but its characteristic movement can be imitated, and so we shall do.
In order to reach another square, whether by movement or capture, an inchworm piece needs to make two moves: the first stretches out to the new square, and the second consolidates the piece onto a single square.
The stretch may be a movement or a capture, but the consolidation can only be that: it cannot be a capture.
A stretched piece may retreat by consolidating back onto the square it first stretched from. Once it has done so, it has moved (twice, in fact); thus, it may neither make the Pawn's two-step move nor participate in Castling.
A stretched piece may be captured on either of the squares it occupies. Please notice that this means an attacked consolidated piece has no escape!
I interpret the en passant rule to mean that a consolidated Pawn that has just finished a two-step move may be captured e.p.
There is no obligation to consolidate a stretched piece.
Rules of Inchworm ChessThe rules of FIDE Chess apply except as follows: all pieces, including King and Pawns, make only inchworm moves and captures; and the 50-moverule must be extended to 100 moves.
With a White Rook on g1 and a Black K on h8, W to play may try Rg1-h1, but Black can respond with Kh8-g8, running away. If in response Rh1-g1, of course Kg8-h8. However, Black to play would be mated: Kh8-h7 Rg1-h1, both consolidate, checkmate.
Endgames with a small number of inchworm pieces sometimes are the same as normal endgames because the stretchings and consolidations can be sequenced.
There are many exceptions. In general, the weaker side loses more often. One reason is that a stretched piece is more vulnerable but a consolidated piece cannot escape, and the second reason is that although a stretched piece does not give check it is fatal for the King to consolidate onto the square it "covers" -- fatal, but legal, so the stalemate defense occurs less frequently (K+N+N versus K is a win).
1. e2-e4 d7-d5 2. e2-e4 d7-d5 3. e4xd5 Qd8xd5xe4 4. Nb1-c3 Qd5-d8
This sample game shows that you cannot manage to make the game seem like normal chess, even if both sides cooperate in sequencing the moves: 4...Qd8-d5 would have lost the Queen because an attacked piece has no escape. However, 4...Qd5-d8 has actually gained a tempo! Compared to book lines in FIDE Chess, Black has chosen an inferior line but has in compensation an extra move.
Inchworm movement appears to be value-preserving and so the author suggests that you ought to play Inchworm Chess with Different Armies.
CritiqueA stretched piece occupies two squares, and therefore Inchworm Chess falls gently into the category of "variants in which one piece may occupy one or many squares". This is a very uncrowded category.
Compared to Tirebiter Chess, Inchworm Chess is gentler and simpler, more playable and more likely to be played. Of course, since a game of Inchworm may take twice as many moves as a game of FIDE Chess, you would not choose to play it by mail nor by email.
A stretched piece cannot capture, and therefore is in two places at once but in one sense is nowhere at all. By being in two places, it threatens to consolidate onto either; and this threat was the reason that I chose to have consolidation done manually instead of allowing it to happen automatically next turn: one may have something more urgent to do than to consolidate, or one may wish to retain the flexibility of being stretched -- after all, a consolidated piece cannot flee from an attacker, but a stretched piece can do so.
Long Worm Chess
In the forests of Pennsylvania one often sees an inchworm, but one never sees a Long Worm. This is easily explained.
The long worm is a fictional creature from a novel, "Dune", that was published in my youth. This novel had some cult following, and as a result the Long Worm became a monster in the game of Hack, around 1982 or so. Now its descendant is nethack, and there is no link here because of course you have www.nethack.org bookmarked already.
The Long Worm is unique. No other monster in Nethack occupies more than one position! How appropriate to today's theme...
The Long Worm is also unique because it comes in varying sizes, and if you attack a large one from the rear you may get a message "You cut off part of the long worm's tail!", and you find yourself fighting a smaller Long Worm.
Rules of Long Worm Chess
- The rules of Inchworm Chess apply except as follows.
- When half a stretched piece is captured, the other half stays on the board as a half piece, as defined by the rules of Half Chess. 
- The half piece is not an inchworm piece. It moves directly to its destination in a single turn, as in FIDE Chess.
- Pawns are too small to be cut in half and still survive. Capturing half a Pawn kills the whole Pawn.
- You're either a King or you're not. Capturing half a stretched King ends the game. One does not say "Long live the half King."
Rule 3 is the key. "The half piece is not an inchworm piece."
The half piece is not an inchworm piece. Is a Halfling Queen worth less than an Inchworm Queen? Is it worth more? Who can say?
In Long Worm Chess, when you are about to capture half of your opponent's stretched piece, your mind will be suffused with a miasma of fear, doubt, and uncertainty. 
Seriously, the tension between the worth of the whole Inchworm piece and the direct-moving Half-Chess piece is the main point of the design of this game. Without rule 3, the idea would be worth mentioning but it would not be potentially a great game.
Yes. It should be played with different armies.
Problem. Half-pieces are not defined for all pieces in all standard armies. The choices must be agreed upon before the start of the game.
Each player has the normal number of pieces on the board at the start of the game, but controls a lineup which contains not only the Inchworm pieces that start the game but also the Half Chess pieces which may potentially appear.
In other words, each player has two different armies. For a game in which each player has four different armies, consider Archoniclastic Long Worm Chess. (You may have trouble doing so, since Archoniclastic Chess hasn't been written yet. Try anyway.)
In other words, each player has two different armies. Would it be so terrible if I started with the Inchworm Colorbound Clobberers and the Half Chess Nutty Knights? In a sense, it is terrible because it violates the metaphor of the piece being cut in half; but legally, it is legal.
 Just as the Alfil and Wazir are basic building blocks of chess pieces, so are Half Chess and Augmented Chess basic buiding blocks of chess variants; and just as a halfling standing on the shoulders of a dwarf may see further than a lame Knight, so equally may we build one folly upon another.
 Suffused? Miasma? All I need to say is
"ichor" and you will think I have been rereading H.P. Lovecraft.
Written by Ralph Betza.
WWW page created: February 24th, 2002.